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import NNG.MyNat.Addition
namespace MyNat
attribute [-simp] MyNat.succ.injEq
example (a b : ℕ) (h : (succ a) = b) : succ (succ a) = succ b := by
simp
sorry
axiom succ_inj {a b : ℕ} : succ a = succ b → a = b