Module Type NZMulProp (Import NZ : NZAxiomsSig')(Import NZBase : NZBaseProp NZ).
Include NZAddProp NZ NZBase.
Hint Rewrite mul_0_r mul_succ_r : nz.
Hint Rewrite mul_1_l mul_1_r : nz.

Theorem mul_shuffle2 : forall n m p q, (n * m) * (p * q) == (n * q) * (m * p).