26 lines
811 B
Text
26 lines
811 B
Text
open decidable
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open eq
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namespace experiment
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inductive nat : Type
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| zero : nat
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| succ : nat → nat
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definition refl := @eq.refl
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namespace nat
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definition pred (n : nat) := nat.rec zero (fun m x, m) n
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theorem pred_zero : pred zero = zero := refl _
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theorem pred_succ (n : nat) : pred (succ n) = n := refl _
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theorem zero_or_succ (n : nat) : n = zero ∨ n = succ (pred n)
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:= nat.induction_on n
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(or.intro_left _ (refl zero))
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(take m IH, or.intro_right _
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(show succ m = succ (pred (succ m)), from congr_arg succ (symm (pred_succ m))))
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theorem zero_or_succ2 (n : nat) : n = zero ∨ n = succ (pred n)
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:= @nat.induction_on _ n
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(or.intro_left _ (refl zero))
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(take m IH, or.intro_right _
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(show succ m = succ (pred (succ m)), from congr_arg succ (symm (pred_succ m))))
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end nat
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end experiment
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