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 combine_wzero : forall sz1 sz2, combine (wzero sz1) (wzero sz2) = wzero (sz1 + sz2).