15 lines
269 B
Text
15 lines
269 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
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(take m IH,
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begin
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refine
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(calc
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0 + succ m = succ (0 + m) : _
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... = succ m : IH),
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esimp
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end)
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