Corollary and_or_distrib_l:
  forall x y z,
  and (or x y) z = or (and x z) (and y z).

(* Specifications: *)
Theorem or_and_distrib: forall x y z, or x (and y z) = and (or x y) (or x z).
Theorem or_and_distrib: forall x y z, or x (and y z) = and (or x y) (or x z).