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lean4game/server/nng/NNG/MyNat/Multiplication.lean

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import NNG.MyNat.Addition
namespace MyNat
open MyNat
def mul : MyNat → MyNat → MyNat
| _, 0 => 0
| a, b + 1 => a + (MyNat.mul a b)
instance : Mul MyNat where
mul := MyNat.mul
axiom mul_zero (a : MyNat) : a * 0 = 0
axiom mul_succ (a b : MyNat) : a * (succ b) = a * b + a