fact: Definition div2_gen (n:nat) : {p:nat | n = p+p}+{p:nat | pred n = p+p} := match test_even n with | left h => inl _ (div2_of_even n h) | right h' => inr _ (div2_of_even (pred n) h') end.
imports: ZArith List Arith Lia Zwf