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                               Nebraska Supreme Court Advance Sheets
                                        306 Nebraska Reports
                                                    TYLER F. v. SARA P.
                                                     Cite as 306 Neb. 397




                           Tyler F., appellant, v. Sara P., appellee.
                      Geoffrey V., as next friend of J.F., a minor child,
                      appellee and cross-appellant, v. Sara P., appellee
                         and cross-appellee, and Tyler F., appellant
                                      and cross-appellee.
                                                        ___ N.W.2d ___

                                        Filed July 10, 2020.     Nos. S-19-513, S-19-514.

                 1. Paternity: Appeal and Error. In a filiation proceeding, questions con-
                    cerning child custody determinations are reviewed on appeal de novo on
                    the record to determine whether there has been an abuse of discretion
                    by the trial court, whose judgment will be upheld in the absence of an
                    abuse of discretion.
                 2. Statutes. Statutory interpretation presents a question of law.
                 3. Judgments: Appeal and Error. When reviewing questions of law, an
                    appellate court has an obligation to resolve the questions independently
                    of the conclusion reached by the trial court.
                 4. Appeal and Error: Words and Phrases. Plain error exists where there
                    is an error, plainly evident from the record, which prejudicially affects
                    a substantial right of a litigant and is of such a nature that to leave it
                    uncorrected would cause a miscarriage of justice or result in damage to
                    the integrity, reputation, and fairness of the judicial process.
                 5. Appeal and Error. An appellate court may, at its option, notice plain
                    error.
                 6. Paternity: Acknowledgments: Rescission: Time. In Nebraska, a pater-
                    nity acknowledgment operates as a legal finding of paternity after the
                    rescission period has expired.
                 7. Paternity: Acknowledgments. Paternity may be established by a
                    properly executed acknowledgment, and establishment of paternity by
                    acknowledgment is the equivalent of establishment of paternity by judi-
                    cial proceeding.
                 8. Parental Rights: Child Custody: Paternity: Acknowledgments: DNA
                    Testing. A father whose paternity is established by a final, voluntary
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             Nebraska Supreme Court Advance Sheets
                      306 Nebraska Reports
                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

      acknowledgment has the same right to seek custody as the child’s
      biological mother, even if genetic testing shows he is not the biologi-
      cal father.
 9.   Paternity: Acknowledgments: DNA Testing. DNA testing which later
      shows the identified individual is not the child’s biological father
      is insufficient to set aside a properly executed acknowledgment of
      paternity.
10.   Paternity: Acknowledgments: Parent and Child. An acknowledgment
      legally establishes paternity and grants the individual named as father
      the legal status of a parent to the child regardless of genetic factors.
11.   Paternity: Statutes. Paternity proceedings are purely statutory, and
      because the statutes regarding paternity proceedings modify the common
      law, they must be strictly construed.
12.   Statutes: Appeal and Error. Statutory language is to be given its plain
      and ordinary meaning, and an appellate court will not resort to inter-
      pretation to ascertain the meaning of statutory words which are plain,
      direct, and unambiguous.
13.   Statutes: Legislature: Intent. Components of a series or collection of
      statutes pertaining to a certain subject matter are in pari materia and
      should be conjunctively considered and construed to determine the
      intent of the Legislature, so that different provisions are consistent, har-
      monious, and sensible.
14.   Paternity: Parties: Acknowledgments. A previous paternity determina-
      tion, including a properly executed and undisturbed acknowledgment,
      must be set aside before a third party’s paternity may be considered.
15.   Paternity. A party seeking to establish paternity must first set aside an
      existing determination.
16.   Acknowledgments: Proof. In order to set aside an unrevoked acknowl-
      edgment, the moving party has the burden to show the acknowledge-
      ment was a result of fraud, duress, or material mistake.
17.   Paternity: Acknowledgments. A party executing an acknowledgment
      of paternity has a duty to exercise reasonable diligence in the execution
      of the acknowledgment to ensure that it was grounded in fact.
18.   Words and Phrases. Reasonable diligence means appropriate action
      where there is some reason to awaken inquiry and direct diligence in a
      channel in which it will be successful.

  Appeals from the District Court for Lancaster County: Kevin
R. McManaman, Judge. Affirmed in part, and in part reversed
and remanded for further proceedings.
   Andrea L. McChesney, of McChesney Family Law Office,
for appellant.
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         Nebraska Supreme Court Advance Sheets
                  306 Nebraska Reports
                       TYLER F. v. SARA P.
                        Cite as 306 Neb. 397

  Joel Bacon and Tara L. Gardner, of Keating, O’Gara, Nedved
& Peter, P.C., L.L.O., for appellee Geoffrey V.
  Heavican, C.J., Miller-Lerman, Cassel, Stacy, Funke,
Papik, and Freudenberg, JJ.
   Funke, J.
   The district court awarded joint legal and physical custody
of J.F. to Sara P., Tyler F., and Geoffrey V. Tyler appealed
and assigned various errors. Geoffrey then cross-appealed. We
conclude that the district court did not err in finding that Sara
failed to meet her burden to set aside the notarized acknowl-
edgment of paternity executed by Tyler and Sara at the time of
J.F.’s birth. We further conclude that the trial court committed
plain error in considering Geoffrey’s paternity complaint while
failing to give proper legal effect to Tyler’s acknowledgment
of paternity. We therefore affirm the court’s denial of Sara’s
counterclaim to set aside Tyler’s acknowledgment of paternity;
reverse the district court’s award of joint legal and physical
custody of J.F. to Sara, Tyler, and Geoffrey; and remand the
cause for further proceedings.
                         BACKGROUND
   Sometime around November 2007, Tyler and Sara were dat-
ing and engaged in sexual intercourse. Sara gave birth to J.F.
in August 2008. Sara continually represented to Tyler that he
was the father of J.F., and Tyler signed an acknowledgment
of paternity at the hospital when J.F. was born and is listed as
J.F.’s father on the birth certificate.
   Sara also engaged in sexual intercourse with Geoffrey
around November 2007. Sara contends she believed Tyler
was J.F.’s father because of information she received from
her physician about her due date. At one point during the
pregnancy, however, she contacted Geoffrey about the pos-
sibility that he might be the father and, about 8 to 9 months
after J.F.’s birth, Geoffrey and Sara had discussions about
genetic testing to determine paternity. Sara testified that she
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         Nebraska Supreme Court Advance Sheets
                  306 Nebraska Reports
                       TYLER F. v. SARA P.
                        Cite as 306 Neb. 397

always had a “gut feeling” that J.F. might not be Tyler’s bio-
logical child and that this “gut feeling” that “maybe he could
be [Geoffrey’s existed] when [Sara] was pregnant, when [J.F.]
was born [and] when [J.F.] started really looking like him.”
It is undisputed she did not tell Tyler about Geoffrey’s pos-
sible paternity.
   Following J.F.’s birth, Tyler and Sara shared parenting
responsibilities despite ceasing their romantic relationship,
even through Sara’s move to Oklahoma in 2013. At the time
of Sara’s move, J.F. was in the middle of his first year of
preschool and the parties agreed J.F. would continue to attend
school in Nebraska and reside with Tyler. After the school year,
in the summer of 2014, Sara indicated to Tyler that she wanted
J.F. to stay with her and attend kindergarten in Oklahoma.
   Extending from the parties’ disagreement concerning J.F.’s
schooling, Tyler filed a complaint to establish paternity, cus-
tody, and parenting time under case No. CI 14-2745, currently
under appeal as case No. S-19-513. In his complaint, Tyler
sought joint legal and physical custody of J.F., as well as an
order determining paternity. Tyler alleged in this complaint that
he “believes he is the biological father of [J.F.] and has always
held himself out as such,” that Sara “has always held [Tyler]
out as [J.F.’s] biological father,” and that Tyler “is listed and
acknowledged on [J.F.’s] birth certificate.”
   In Sara’s answer and counterclaim, she alleged that Tyler
is not J.F.’s biological father and that he has no standing to
request custody of J.F. As such, Sara sought, in part, that the
district court dismiss Tyler’s complaint, declare Tyler not to be
the biological father of J.F., and award Sara sole physical and
legal custody.
   During the proceedings, the court ordered DNA testing that
showed Tyler was not J.F.’s biological father. Following receipt
of the testing results, Sara amended her answer and counter-
claim, seeking, among other things, an order rescinding Tyler’s
acknowledgment of paternity on the ground of mutual mistake
and disestablishing paternity.
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         Nebraska Supreme Court Advance Sheets
                  306 Nebraska Reports
                        TYLER F. v. SARA P.
                         Cite as 306 Neb. 397

    Shortly after the DNA test excluded Tyler as the biological
father, Sara reached out to Geoffrey and told him she believed
he was the father. Geoffrey then filed a motion to intervene in
Tyler’s case, seeking intervention as the “biological father of
[J.F.]” However, the court denied Geoffrey’s motion because
Geoffrey provided no basis to avoid the 4-year statute of
limitations under Neb. Rev. Stat. § 43-1411 (Reissue 2016) and
did not allege he was unaware of J.F.’s birth or the possibility
of paternity.
    Thereafter, Geoffrey filed a complaint to establish pater-
nity under case No. CI 15-119, currently under appeal as case
No. S-19-514, seeking that physical and legal custody be placed
with Sara subject to his and Tyler’s visitation rights. Geoffrey’s
complaint acknowledged Tyler as J.F.’s legal father, referenc-
ing Tyler’s acknowledgment of paternity, and explained that
Geoffrey was not made aware he was J.F.’s biological father
until October 2014, when Sara told him about the results of
Tyler’s DNA test. The complaint’s caption listed “Geoffrey [V.],
as next friend of [J.F.], a minor child,” as plaintiff. However,
the text of the complaint and the signature line at the end of
the complaint described only Geoffrey, individually, without
mentioning his status as next friend of J.F. Geoffrey also noted
that genetic testing established Tyler was not the biologi-
cal father and alleged that Tyler’s belief he was the biological
father was “based on the material mistake of fact based on the
representations of Sara . . . at the time [J.F.] was conceived
and born.” Geoffrey claimed, “The presumption that . . . Tyler
. . . is the father of [J.F.], through his signed Acknowledgment
of Paternity, has been rebutted through genetic testing and the
records of the Nebraska Department of Health and Human
Services should be corrected.”
    Tyler filed an answer to Geoffrey’s complaint. In his answer,
Tyler requested the court dismiss the complaint insofar “as
the matter has already been decided in Case No. CI14-2745.”
The answer did not specifically raise any statute of limita-
tions defenses.
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            Nebraska Supreme Court Advance Sheets
                     306 Nebraska Reports
                            TYLER F. v. SARA P.
                             Cite as 306 Neb. 397

   The court consolidated cases Nos. CI 14-2745 and CI 15-119,
held a trial, and entered an order in January 2016. The court
determined that Geoffrey had standing to act in the capacity
of next friend of J.F., that Tyler is the father of J.F. by reason
of the acknowledgment of paternity, and that Geoffrey is the
father of J.F. by reason of biological testing. The court found
Sara failed to meet her burden to establish mutual mistake
and denied her motion to set aside Tyler’s acknowledgment.
The court, therefore, considered the rights and interests of
Tyler, Geoffrey, and Sara in making custody, parenting time,
and child support determinations. The court awarded legal
and physical custody of J.F. to Tyler, subject to visitation with
Geoffrey and Sara, until December 31, 2016, at which time all
three parties were awarded joint legal and physical custody.
The court also calculated child support by considering the
incomes of Tyler, Geoffrey, and Sara and ordered Geoffrey and
Sara to pay child support until December 31, when all support
obligations were to cease.
   Tyler appealed, assigning the district court erred in finding
that Geoffrey had standing to bring his claim as next friend of
J.F. and in deviating from the child support guidelines in set-
ting child support. Geoffrey cross-appealed and assigned that
the court erred in concluding he had not raised a claim in his
individual capacity and, to the extent the appellate court might
conclude Tyler’s paternity acknowledgment had to be set aside
before determining that Geoffrey had paternity, that the court
erred in evaluating the material mistake of fact question from
Sara’s perspective.
   The Nebraska Court of Appeals reversed the district court’s
order. 1 First, the Court of Appeals determined Geoffrey lacked
standing to raise any claims on J.F.’s behalf, as J.F.’s next
friend, because J.F. was in the custody of Sara, his biologi-
cal mother, and Tyler, his legal father, and thus not without
a guardian. However, the appellate court found that the trial
1
    Tyler F. v. Sara P., 24 Neb. App. 370, 888 N.W.2d 537 (2016).
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         Nebraska Supreme Court Advance Sheets
                  306 Nebraska Reports
                        TYLER F. v. SARA P.
                         Cite as 306 Neb. 397

court failed to address whether Geoffrey was also bringing
his claims in his individual capacity. As such, the cause was
remanded to the district court for determination of whether
Geoffrey also brought his claims in his individual capacity
and whether such individual claims are barred by the statute
of limitations.
   On remand, the district court found that Geoffrey had
brought his claims in both his individual capacity and as J.F.’s
next friend due to the language and intended beneficiary of
the complaint. The court then found that Geoffrey’s individual
claims were not barred by the statute of limitations, because
Tyler waived the defense by failing to assert it in his answer
or another responsive pleading. The court found that even if
Tyler had not waived the statute of limitations, it was tolled
because Geoffrey alleged he was not made aware he was J.F.’s
biological father until October 2014 and Tyler’s answer did
not sufficiently deny this allegation. Similarly, the court deter-
mined that res judicata did not bar Geoffrey’s claims due to the
court’s denial of Geoffrey’s motion to intervene, because Tyler
failed to raise it as an affirmative defense and because even if
he had, res judicata was inapplicable to the instant case. Given
the court’s finding that Geoffrey also brought his claims in
his individual capacity, the court reinstated its previous order
“with the caveat that the order applies to [Geoffrey] individ­
ually rather than as next friend of J.F.”
                  ASSIGNMENTS OF ERROR
   Tyler assigns, restated, that the district court erred in (1)
finding Geoffrey brought his claims in his individual capac-
ity, (2) finding Tyler waived the statute of limitations defense,
(3) finding the statute of limitations was tolled, (4) finding
Geoffrey’s claims were not barred by the denial of his motion
to intervene, (5) failing to find Geoffrey’s claims were time-
barred, and (6) deviating from the child support guidelines in
the custody award.
   On cross-appeal, Geoffrey assigns, contingent on a find-
ing of plain error in the district court’s conclusion that Tyler’s
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            Nebraska Supreme Court Advance Sheets
                     306 Nebraska Reports
                            TYLER F. v. SARA P.
                             Cite as 306 Neb. 397

paternity acknowledgment did not have to be set aside before
the district court could determine whether Geoffrey had pater-
nity, that the court erred in failing to set aside Tyler’s paternity
acknowledgment.
                   STANDARD OF REVIEW
   [1] In a filiation proceeding, questions concerning child
custody determinations are reviewed on appeal de novo on the
record to determine whether there has been an abuse of discre-
tion by the trial court, whose judgment will be upheld in the
absence of an abuse of discretion. 2
   [2,3] Statutory interpretation presents a question of law. 3
When reviewing questions of law, an appellate court has an
obligation to resolve the questions independently of the conclu-
sion reached by the trial court. 4
                            ANALYSIS
                Acknowledgment of Paternity
   Before reaching the assigned errors, we first address the
question of whether the district court committed plain error
in determining it unnecessary to set aside Tyler’s paternity
acknowledgment before considering Geoffrey’s complaint to
establish paternity.
   [4,5] Plain error exists where there is an error, plainly evi-
dent from the record, which prejudicially affects a substantial
right of a litigant and is of such a nature that to leave it uncor-
rected would cause a miscarriage of justice or result in damage
to the integrity, reputation, and fairness of the judicial process. 5
An appellate court may, at its option, notice plain error. 6
2
    State on behalf of Kaaden S. v. Jeffery T., 303 Neb. 933, 932 N.W.2d 692
    (2019).
3
    Fetherkile v. Fetherkile, 299 Neb. 76, 907 N.W.2d 275 (2018).
4
    Id.
5
    See, In re Application No. OP-0003, 303 Neb. 872, 932 N.W.2d 653
    (2019); Osantowski v. Osantowski, 298 Neb. 339, 904 N.W.2d 251 (2017).
6
    Mays v. Midnite Dreams, 300 Neb. 485, 915 N.W.2d 71 (2018).
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            Nebraska Supreme Court Advance Sheets
                     306 Nebraska Reports
                            TYLER F. v. SARA P.
                             Cite as 306 Neb. 397

   When J.F. was born, Tyler and Sara signed a notarized
acknowledgment of paternity in which they attested that Tyler
was J.F.’s biological father. Although Sara’s amended answer
and counterclaim sought to set aside this acknowledgment fol-
lowing the court-ordered DNA test that showed Tyler was not
J.F.’s biological father, the district court declined to do so, find-
ing Sara failed to meet her burden to prove a material mistake
of fact had occurred. As such, the court found the acknowledg-
ment remains in effect. However, the court went on to deter-
mine that it could consider Geoffrey’s simultaneous claim of
paternity without setting aside Tyler’s acknowledgment. The
court then found that both Tyler and Geoffrey were the fathers
of J.F. and that Sara retained the position of mother under the
paternity statutes.
   [6] In Nebraska, a paternity acknowledgment operates
as a legal finding of paternity after the rescission period
has expired. 7 The proper legal effect of a signed, notarized
acknowledgment of paternity is a finding that the individual
who signed as the father is in fact the legal father. 8 Neb. Rev.
Stat. § 43-1409 (Reissue 2016) establishes this legal effect
and provides:
         The signing of a notarized acknowledgment, whether
      under section 43-1408.01 or otherwise, by the alleged
      father shall create a rebuttable presumption of paternity as
      against the alleged father. The signed, notarized acknowl-
      edgment is subject to the right of any signatory to rescind
      the acknowledgment within the earlier of (1) sixty days
      or (2) the date of an administrative or judicial proceeding
      relating to the child, including a proceeding to establish a
      support order in which the signatory is a party. After the
      rescission period a signed, notarized acknowledgment is
      considered a legal finding . . . .
7
    In re Adoption of Jaelyn B., 293 Neb. 917, 883 N.W.2d 22 (2016); Cesar
    C. v. Alicia L., 281 Neb. 979, 800 N.W.2d 249 (2011).
8
    Cesar C., supra note 7.
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             Nebraska Supreme Court Advance Sheets
                      306 Nebraska Reports
                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

   [7] Relatedly, in describing child support obligations of the
parents, Neb. Rev. Stat. § 43-1402 (Reissue 2016) refers to
“[t]he father of a child whose paternity is established either by
judicial proceedings or by acknowledgment as hereinafter pro-
vided . . . .” We have explained that this language in § 43-1402
contemplates that paternity may be established by a properly
executed acknowledgment and that establishment of paternity
by acknowledgment is the equivalent of establishment of pater-
nity by judicial proceeding. 9
   [8] Reading §§ 43-1402 and 43-1409 together, the provi-
sion in § 43-1409 that an acknowledgment is a “legal finding”
means that a properly executed acknowledgment legally estab-
lishes paternity in the person named in the acknowledgment as
the father. 10 A father whose paternity is established by a final,
voluntary acknowledgment has the same right to seek custody
as the child’s biological mother, even if genetic testing shows
he is not the biological father. 11
   Here, it is undisputed that the acknowledgment of paternity
signed by Tyler and Sara was properly executed. Additionally,
there is no evidence that either party to the acknowledgment
sought to rescind it within the statutory rescission period. The
acknowledgment remained in full force and effect at the time
of Tyler’s paternity action and legally determined Tyler’s pater-
nity of J.F. As such, upon finding that the notarized acknowl-
edgment of paternity had been properly signed, the court
should have treated Tyler’s paternity as having been legally
established and treated this action as one solely to determine
issues of custody and support as between two legal parents,
and not one to establish paternity. 12
   [9,10] In her answer and counterclaim, Sara alleged Tyler
was neither the legal nor the biological father of J.F. As a
 9
     See id.
10
     See id.
11
     In re Adoption of Jaelynn B., supra note 7.
12
     See Cesar C., supra note 7.
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             Nebraska Supreme Court Advance Sheets
                      306 Nebraska Reports
                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

result, she sought DNA testing to confirm her allegations.
However, the Legislature has established that a properly exe-
cuted acknowledgment of paternity cannot be set aside merely
by DNA testing which later shows the identified individual is
not the child’s biological father. 13 While § 43-1412.01 provides
that “[a]n individual may file a complaint for relief and the
court may set aside a final judgment . . . or any other legal
determination of paternity if a scientifically reliable genetic
test . . . establishes the exclusion of the individual named as a
father in the legal determination,” it further clarifies that “[a]
court shall not grant relief from determination of paternity
if the individual named as father . . . completed a notarized
acknowledgment of paternity . . . .” We have found that this
provision provides further support for the conclusion that an
acknowledgment legally establishes paternity and grants the
individual named as father the legal status of a parent to the
child regardless of genetic factors. 14 Because Tyler’s acknowl-
edgment remained in full force and effect and established his
paternity of J.F. regardless of genetic factors, the trial court had
no basis to order the DNA testing.
   That is not to say an acknowledgment cannot be challenged
and set aside, but the grounds for doing so are limited. Section
43-1409 explains that a properly executed acknowledgment
“may be challenged only on the basis of fraud, duress, or
material mistake of fact with the burden of proof upon the
challenger.” Therefore, under the statutory scheme, before Sara
could challenge paternity and subject Tyler to genetic test-
ing, she needed to overcome the acknowledgment establishing
Tyler was J.F.’s legal father by showing fraud, duress, or mate-
rial mistake. 15
   Following the inappropriately ordered DNA test, Sara
amended her answer and counterclaim to seek to set aside
13
     See, Neb. Rev. Stat. § 43-1412.01 (Reissue 2016); Cesar C., supra note 7.
14
     In re Adoption of Jaelyn B., supra note 7.
15
     See, id.; Cesar C., supra note 7.
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               Nebraska Supreme Court Advance Sheets
                        306 Nebraska Reports
                          TYLER F. v. SARA P.
                           Cite as 306 Neb. 397

the acknowledgment of paternity. Sara claimed both parties
thereto had been under a material mistake of fact due to her
being informed of an “erroneous due date by her treating phy-
sician.” Sara specifically alleged that her projected due date
was August 11, 2008, from which she believed Tyler was the
father based upon a 9-month gestation period, but that this
due date was incorrect and that labor was induced several
days earlier.
   In its order declining to set aside the acknowledgment,
the court correctly considered the issue without concern to
the results of the DNA test. The court found that there was
clear evidence Sara knew of the possibility Tyler was not the
father during and following pregnancy and that even though
Tyler was under the mistaken belief he was J.F.’s biological
father, it was Sara’s burden as the challenger to show a mate-
rial mistake on her part, which she did not. Because the court
declined to set the acknowledgment aside, it remains in full
force and effect.
          Geoffrey’s Determination of Paternity
   Geoffrey’s complaint to establish his paternity of J.F. alleges
that Geoffrey did not know he was J.F.’s father until Sara
informed him that DNA testing excluded Tyler as J.F.’s bio-
logical father. Regardless of whether that allegation is sup-
ported by the record, as noted above, the court had no basis to
order this test, due to the application of the acknowledgment
of paternity. 16
   Further, Geoffrey’s complaint fails to move for Tyler’s
acknowledgment of paternity to be set aside. Instead, Geoffrey
argues, and the district court agreed, that a determination that
Tyler has paternity of J.F. is of no consequence when deter-
mining whether Geoffrey has paternity of J.F. However, this
proposition is at odds with Nebraska’s paternity and related
statutes and the Nebraska Child Support Guidelines as cur-
rently constructed.
16
     See id.
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             Nebraska Supreme Court Advance Sheets
                      306 Nebraska Reports
                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

   [11-13] We have recognized that paternity proceedings
are purely statutory and that because the statutes regarding
paternity proceedings modify the common law, they must be
strictly construed. 17 Statutory language is to be given its plain
and ordinary meaning, and an appellate court will not resort
to interpretation to ascertain the meaning of statutory words
which are plain, direct, and unambiguous. 18 Components of a
series or collection of statutes pertaining to a certain subject
matter are in pari materia and should be conjunctively consid-
ered and construed to determine the intent of the Legislature,
so that different provisions are consistent, harmonious,
and sensible. 19
   Actions to determine paternity and parental support are gov-
erned by Neb. Rev. Stat. §§ 43-1401 through 43-1418 (Reissue
2016 & Cum. Supp. 2018). Throughout these statutes, the
Legislature has used language which recognizes the possibil-
ity of only a singular paternity determination. For example,
§ 43-1402 describes “[t]he father of a child whose paternity is
established,” “[t]he mother of a child,” and “each parent” in
explaining support liability for a child. (Emphasis supplied.)
Section 43-1403 describes possible county obligations of sup-
port “[i]n case of the neglect or inability of the parents, or
either of them, to support a child . . . .” (Emphasis supplied.)
Section 43-1404 designates the “liability of the father or
mother of a child for its support” in explaining the discharge of
support obligations. (Emphasis supplied.) Section 43-1405 uses
the singular “the father” language several times in describing
the discharge of support liability by settlement. (Emphasis
supplied.) Section 43-1407 identifies “[t]he father of a child”
in its explanation of liability for birth, pregnancy, and medi-
cal expenses. (Emphasis supplied.) Section 43-1410 explains,
“Any judicially approved settlement or order of support made
17
     State on behalf of B.M. v. Brian F., 288 Neb. 106, 846 N.W.2d 257 (2014).
18
     In re Application No. OP-0003, supra note 5.
19
     Id.
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             Nebraska Supreme Court Advance Sheets
                      306 Nebraska Reports
                           TYLER F. v. SARA P.
                            Cite as 306 Neb. 397

by a court having jurisdiction in the premises shall be bind-
ing on the legal representatives of the father or mother in the
event of his or her death . . . .” (Emphasis supplied.) Section
43-1412(3), in explaining a court’s continued jurisdiction of a
paternity action to order support and court costs, states:
      If a judgment is entered under this section declaring the
      alleged father to be the father of the child, the court shall
      retain jurisdiction of the cause and enter such order of
      support, including the amount, if any, of any court costs
      and attorney’s fees which the court in its discretion deems
      appropriate to be paid by the father . . . .
(Emphasis supplied.)
   Statutes under Nebraska’s Parenting Act 20 use similar lim-
iting language. Section 43-2922(12) describes the existence
of only two parents and defines “[j]oint physical custody” as
“mutual authority and responsibility of the parents regarding
the child’s place of residence and the exertion of continuous
blocks of parenting time by both parents over the child for
significant periods of time.” (Emphasis supplied.) This “both
parents” language is used in other parts of the Parenting Act,
including the following sections: § 43-2924(2), in describing
the applicability of the Parenting Act for custody determina-
tions; § 43-2929(4), in explaining that both parents continue
to have parental rights regardless of a custody determina-
tion in a parenting plan unless the rights are terminated; and
§ 43-2937(4), in describing when court-ordered mediation or
alternative dispute resolution is required under the Parenting
Act. Relatedly, § 43-2930(1) lists permissible information
a child information affidavit may include when certain cir-
cumstances are present, including “criminal no-contact orders
against either parent.” (Emphasis supplied.) The language of
§ 43-2932 considers the existence of only two parents in the
requirements under subsection (1)(a)(iv) that a court develop
20
     See Neb. Rev. Stat. §§ 43-2920 to 43-2943 (Reissue 2016, Cum. Supp.
     2018 & Supp. 2019).
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                             TYLER F. v. SARA P.
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a parenting plan if “a parent . . . has interfered persistently
with the other parent’s access to the child;” under subsection
(1)(b)(iv) of additional permissible limitations of a parenting
plan, including “[r]estraints on the parent from communica-
tion with or proximity to the other parent or the child;” and
under subsection (3) that the “parent found to have engaged in
the behavior . . . has the burden of proving” the rights granted
under the parenting plan “will not endanger the child or the
other parent.” (Emphasis supplied.)
   We are mindful that following the U.S. Supreme Court’s
decision in Obergefell v. Hodges, 21 our courts are now hear-
ing cases involving two legal mothers or two legal fathers.
But our current parentage statutes have not changed, and
these statutes are still gender based, so the language of our
opinion is necessarily gender based as well. In other words,
Nebraska’s statutory scheme on parentage accommodates only
two parents and primarily refers to one mother and one father.
Here, the trial judge recognized three legal parents (one
mother and two fathers), and that is simply not suppported by
Nebraska law.
   The Nebraska Child Support Guidelines also use language
which assumes the existence of only a singular paternity deter-
mination, including the identifiers “both parents,” “either par-
ent,” and “both parties.” 22 Though Nebraska’s judicial branch
has revised its child support guidelines to be gender neu-
tral, even the revised guidelines still accommodate just two
legal parents.
   [14] In considering the plain language of our paternity
and related statutes, the Legislature’s use of the singular “the
father” indicates an intention that there can only be one pater-
nity designation at a time, and the use of “both parents,”
21
     Obergefell v. Hodges, ___ U.S. ___, 135 S. Ct. 2584, 192 L. Ed. 2d 609
     (2015).
22
     See, e.g., Neb. Ct. R. § 4-201; Neb. Ct. R. §§ 4-203, 4-204, 4-206, and
     4-215 (rev. 2020); Neb. Ct. R. § 4-214 (rev. 2016).
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                               TYLER F. v. SARA P.
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“either parent,” “either party,” and “both parties” supports
this reading. Accordingly, we hold that a previous paternity
determination, including a properly executed and undisturbed
acknowledgment, must be set aside before a third party’s pater-
nity may be considered.
   To find that one paternity determination has no effect on
subsequent claims of paternity would render our decision in
Cesar C. v. Alicia L. 23 inconsequential. In Cesar C., we deter-
mined that a mother’s request for DNA testing of the acknowl-
edged father to determine whether he was actually the child’s
biological father should have been denied by the trial court
because the acknowledgment of paternity was undisturbed and
properly executed. As such, there was already a determination
of paternity of the child at issue and there could not be another
action to determine paternity without first setting aside the
acknowledgment. 24
   [15] Our holding in Cesar C. applies to the instant case
because just like the mother in Cesar C., Sara sought another
paternity determination even though an acknowledgment
remained applicable, the court failed to give adequate weight to
the undisturbed acknowledgment and inappropriately ordered
DNA testing for the purposes of establishing the child’s pater-
nity, and the DNA test established the legal father was not the
child’s biological father. Herein, Geoffrey then filed a com-
plaint to establish his paternity based upon the DNA results
communicated to him by Sara and did not seek to set aside
the acknowledgment. If the paternity statutes allow for another
party to establish simultaneous paternity without setting aside
a properly executed acknowledgment of paternity, the DNA
tests in Cesar C. and in this case would not be prohibited
because they would provide a basis for a third party to seek
such a simultaneous paternity ruling. However, in line with
our opinion in Cesar C. and as analyzed above, the paternity
23
     Cesar C., supra note 7.
24
     Id.
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                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

statutes require that a party seeking to establish paternity must
first set aside an existing determination.
   Other courts have come to this same conclusion. 25 In Barr
v. Bartolo, 26 the Pennsylvania Superior Court analyzed whether
an undisturbed previous support order barred a subsequent
determination of paternity in a third party. Under Pennsylvania
law, the entry of a court order for support of a child necessarily
determines the alleged father’s paternity. 27 As such, the support
order judicially determined paternity in the husband and the
court held that the previous determination barred relitigation of
paternity without striking that first determination. 28
   In Sinicropi v. Mazurek, 29 the Michigan Court of Appeals
considered what effect an unrevoked acknowledgment of pater-
nity would have on an action to establish paternity. The trial
evidence indicated that the biological father was seeking to
establish his paternity of the minor child after the legal father
had previously executed an unrevoked acknowledgment of
paternity. 30 In granting the biological father’s complaint to
establish paternity, the trial court effectively ruled that the child
had two legal fathers. 31 On appeal, the appellate court reversed
and held that an order of filiation cannot be entered if a proper
acknowledgment of parentage was previously executed and
has not been revoked. 32 The court further held that an unre-
voked acknowledgment already legally established paternity
and conferred the status of natural and legal father upon the
man executing the acknowledgment, which in turn entitled him
25
     Barr v. Bartolo, 927 A.2d 635 (Pa. Super. 2007); Sinicropi v. Mazurek, 273
     Mich. App. 149, 729 N.W.2d 256 (2006).
26
     Barr, supra note 25.
27
     Id.
28
     Id.
29
     Sinicropi, supra note 25.
30
     Id.
31
     Id.
32
     Id.
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                         TYLER F. v. SARA P.
                          Cite as 306 Neb. 397

to seek custody or parenting time if desired and obligated him
to pay support if appropriate. 33
   In accordance with all of the above, the district court
committed plain error in considering Geoffrey’s complaint to
establish his paternity of J.F. when Tyler’s acknowledgment
remained in place and established Tyler as J.F.’s father.

                    Geoffrey’s Cross-Appeal
   In his cross-appeal, Geoffrey acknowledges the possibil-
ity that the district court committed plain error in finding his
paternity without seeking to set aside Tyler’s acknowledgment
of paternity. As such, Geoffrey assigns the district court erred
in failing to set aside the acknowledgment. Geoffrey claims the
court incorrectly limited its consideration of whether a material
mistake of fact occurred to Sara’s perspective, instead of con-
sidering it from his perspective.
   We note that Geoffrey did not independently move the court
to set aside Tyler’s acknowledgment. Instead, his complaint
to establish paternity merely referenced Sara’s allegation that
Tyler’s belief that he was the biological father was based on a
material mistake of fact. Specifically, Geoffrey alleged:
      Genetic testing was completed establishing that
      Tyler . . . is not the father of [J.F.] [Tyler’s] belief that
      he was the father of [J.F.] was based on the representa-
      tions of Sara . . . , and . . . said reliance was based on
      the material mistake of fact based on the representations
      of Sara . . . at the time [J.F.] was conceived and born.
      The presumption that . . . Tyler . . . is the father of [J.F.],
      through his signed Acknowledgment of Paternity, has
      been rebutted through genetic testing and the records of
      the Nebraska Department of Health and Human Services
      should be corrected.
   As a result, we consider Sara’s prayer in her amended
answer that the district court rescind Tyler’s acknowledgment
33
     Id.
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                        TYLER F. v. SARA P.
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of paternity. Specifically, in the “Affirmative Defenses” section
of her amended answer, Sara alleges:
      [J.F.] was born at the Bryan LGH Medical Center East in
      August of 2008. [Sara] was initially informed of an erro-
      neous due date by her treating physician. The initial due
      date was projected to be on August 11, 2008. Based on
      the due date provided to [Sara], she mistakenly believed
      that Tyler . . . was the father of [J.F.] based on a 9 month
      gestation period. However, the anticipated due date was
      incorrect and labor was induced [several days earlier].
      Accordingly, the parties hereto were under a material mis-
      take of fact as [to] the biological father of [J.F.]
Additionally, under a section titled “Counterclaim: Custody,”
Sara alleged: “The Acknowledgment of Paternity executed by
[Tyler and Sara] herein was executed under a material mis-
take of fact precipitated by an inaccurate due date provided
to [Sara]. To the extent the Acknowledgment of Paternity
is rescinded the legal determination of paternity should be
set aside.”
   [16] As explained above, in order to set aside an unrevoked
acknowledgment, the moving party has the burden to show
the acknowledgment was a result of fraud, duress, or material
mistake. 34 Sara, as the challenging party, had the duty to show
that the acknowledgment resulted from a material mistake as
she claimed. 35 In our review, we therefore evaluate the district
court’s decision not to set aside the acknowledgment based
upon Sara’s allegation that there was a material mistake of fact
in the execution of the acknowledgment by Tyler and Sara as
the executing parties, and not from Geoffrey’s perspective as a
nonexecuting party.
   In seeking to set aside Tyler’s paternity, Sara alleged only
that she was under a material mistake of fact that Tyler was the
biological father because her treating physician projected her
34
     § 43-1409.
35
     See id.
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                              TYLER F. v. SARA P.
                               Cite as 306 Neb. 397

due date to be on August 11, 2008, when J.F. was actually born
several days earlier. Based upon this projected due date, Sara
calculated a 9-month gestation period and allegedly believed
Tyler was the biological father.
   The record contradicts Sara’s allegation that she was under
the mistaken belief as to J.F.’s biological father because she
was told this incorrect due-date projection. If Sara received an
incorrect projection of her due date, the due date was no longer
at issue when J.F. was born, as Sara herself indicated when she
testified Tyler should have known he was not the biological
father due to J.F.’s date of birth.
   The record also demonstrates that Sara knew of the possibil-
ity Geoffrey was the biological father during her pregnancy.
Sara contacted Geoffrey about this possibility during the preg-
nancy and again 8 to 9 months after J.F.’s birth. Sara testified
that she always believed that Geoffrey, instead of Tyler, might
be J.F.’s biological father. Geoffrey and Sara talked soon after
J.F. was born about performing genetic testing to determine
whether Geoffrey was the father, but neither took any fur-
ther action.
   [17,18] It is clear that Sara knew Geoffrey could be J.F.’s
biological father, even after being told the projected due date,
and she communicated such possibility to Geoffrey. Due to
this known possibility, Sara had a duty to exercise reason-
able diligence in the execution of the acknowledgment of
Tyler’s paternity to ensure that it was grounded in fact. 36 We
have explained that reasonable diligence “‘means appropri-
ate action where there is some reason to awaken inquiry and
direct diligence in a channel in which it will be successful.’” 37
However, there is no evidence in the record that Sara exer-
cised such reasonable diligence beyond her communications
36
     See Alisha C. v. Jeremy C., 283 Neb. 340, 808 N.W.2d 875 (2012).
37
     Id. at 346, 808 N.W.2d at 881. See, also, DeVaux v. DeVaux, 245 Neb. 611,
     514 N.W.2d 640 (1994) (superseded by statute on other grounds as stated
     in Alisha C., supra note 36).
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                       TYLER F. v. SARA P.
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with Geoffrey. As such, the district court did not err in finding
Sara failed to meet her burden and denying her motion to set
aside Tyler’s acknowledgment.
   Considering all of the above, the district court’s finding
that Sara, and Geoffrey in support of Sara’s motion, failed to
show the alleged material mistake of fact is supported by the
record. Accordingly, the district court’s denial of Sara’s motion
to set aside Tyler’s acknowledgment of his paternity of J.F.
is affirmed.
                         CONCLUSION
   The district court did not err in finding that Sara failed to
meet her burden to set aside the notarized acknowledgment
of paternity executed by Tyler and Sara at the time of J.F.’s
birth. Additionally, a previous paternity determination, includ-
ing a properly executed and undisturbed acknowledgment of
paternity, must be set aside before a third party’s paternity may
be considered. As a result, the district court committed plain
error considering Geoffrey’s paternity complaint while fail-
ing to give proper legal effect to Tyler’s acknowledgment of
paternity. Accordingly, we affirm the court’s denial of Sara’s
counterclaim to set aside Tyler’s acknowledgment of paternity;
reverse the district court’s award of joint legal and physical
custody of J.F. to Sara, Tyler, and Geoffrey; and remand the
cause for further proceedings.
              Affirmed in part, and in part reversed and
              remanded for further proceedings.
