19 lines
539 B
Text
19 lines
539 B
Text
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import data.list
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open list bool nat
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definition filter {A} : list A → (A → bool) → list A
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| filter [] p := []
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| filter (a :: l) p :=
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match p a with
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| tt := a :: filter l p
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| ff := filter l p
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end
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example : list ℕ := filter [0, 3, 7, 2, 4, 6, 3, 4]
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(λ(n : ℕ), begin induction n, exact tt, induction v_0, exact tt, exact ff end)
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definition foo : list ℕ := filter [0, 3, 7, 2, 4, 6, 3, 4]
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(λ(n : ℕ), begin induction n, exact tt, induction v_0, exact tt, exact ff end)
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example : foo = [0, 2, 4, 6, 4] := rfl
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