25 lines
467 B
Text
25 lines
467 B
Text
exit
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open nat
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open eq.ops
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inductive even : nat → Prop :=
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| even_zero : even zero
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| even_succ_of_odd : ∀ {a}, odd a → even (succ a)
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with odd : nat → Prop :=
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| odd_succ_of_even : ∀ {a}, even a → odd (succ a)
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example : even 1 → false :=
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begin
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intro He1,
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cases He1 with [a, Ho0],
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cases Ho0
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end
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example : even 3 → false :=
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begin
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intro He3,
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cases He3 with [a, Ho2],
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cases Ho2 with [a, He1],
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cases He1 with [a, Ho0],
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cases Ho0
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end
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