8 lines
241 B
Text
8 lines
241 B
Text
open nat
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protected theorem my_add_comm : ∀ (n m : ℕ), n + m = m + n
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| n 0 := eq.symm (nat.zero_add n)
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| n (m+1) :=
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suffices succ (n + m) = succ (m + n), from
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eq.symm (succ_add m n) ▸ this,
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congr_arg succ (my_add_comm n m)
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