11 lines
263 B
Text
11 lines
263 B
Text
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import data.nat.basic
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open nat
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theorem zero_left (n : ℕ) : 0 + n = n :=
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nat.induction_on n
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!add.zero_right
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(take m IH, show 0 + succ m = succ m, from
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calc
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0 + succ m = succ (0 + m) : add.succ_right
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... = succ m : IH)
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