Fact eq_rect_combine_dist_helper1 : forall a b c d, b * c = d -> (a + b) * c = a * c + d.Fact eq_rect_combine_dist_helper2 : forall a b c d, b * c = d -> a * c + d = (a + b) * c.

Theorem drop_sub : forall sz n k, (k * pow2 sz <= n)%nat -> natToWord sz (n - k * pow2 sz) = natToWord sz n.