Corollary xor_zero_l: forall x, xor zero x = x.

Theorem rolm_rolm: forall x n1 m1 n2 m2, Z.divide zwordsize modulus -> rolm (rolm x n1 m1) n2 m2 = rolm x (modu (add n1 n2) iwordsize) (and (rol m1 n2) m2).