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    <p>I didn't try, but how about pattern match on y, for example in a
      with-clause? Then the proof should be refl.<br>
    </p>
    <br>
    <div class="moz-cite-prefix">On 2017-07-03 15:34, v0id_NULL wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAE3YR0Xf2M1hV8St1BcjyswNQrUSckfCnzd1cDu3sNbW26E5xQ@mail.gmail.com">
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        <div style="font-size:12.8px">Dear list,</div>
        <div style="font-size:12.8px"><br>
        </div>
        <div style="font-size:12.8px">Help me please. How can I prove
          type of p2?</div>
        <div style="font-size:12.8px"><br>
        </div>
        <div>
          <div><span style="font-size:12.8px">module M1 where</span></div>
          <div><span style="font-size:12.8px"><br>
            </span></div>
          <div>
            <div><span style="font-size:12.8px">open import Data.Nat
                using (ℕ)</span></div>
            <div><span style="font-size:12.8px">open import Data.Bool
                using (Bool; true; false)</span></div>
            <div><span style="font-size:12.8px">open import
                Relation.Binary.PropositionalEquality using (_≡_; refl)</span></div>
            <div><span style="font-size:12.8px"><br>
              </span></div>
            <div><span style="font-size:12.8px">f : Bool → Bool → ℕ</span></div>
            <div><span style="font-size:12.8px">f true x = 1</span></div>
            <div><span style="font-size:12.8px">f y false = 2</span></div>
            <div><span style="font-size:12.8px">f false true = 3</span></div>
            <div><span style="font-size:12.8px"><br>
              </span></div>
            <div><span style="font-size:12.8px">p1 : {x : Bool} → f true
                x ≡ 1</span></div>
            <div><span style="font-size:12.8px">p1 = refl</span></div>
            <div><span style="font-size:12.8px"><br>
              </span></div>
            <div><span style="font-size:12.8px">p2 : {y : Bool} → f y
                false ≡ 2</span></div>
            <div><span style="font-size:12.8px">p2 = {!!}</span></div>
            <div><span style="font-size:12.8px"><br>
              </span></div>
            <div><span style="font-size:12.8px">p3 : f false true ≡ 3</span></div>
            <div><span style="font-size:12.8px">p3 = refl</span></div>
          </div>
        </div>
        <div><br>
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      <pre wrap="">_______________________________________________
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</pre>
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