Fact eq_rect_bitwp' : forall a b Heq f w1 w2,
eq_rect b word (bitwp f w1 w2) a Heq = bitwp f (eq_rect b word w1 a Heq) (eq_rect b word w2 a Heq).
Fact eq_rect_bitwp_1 : forall a b Heq f w1 w2,
bitwp f (eq_rect a word w1 b Heq) w2 = eq_rect a word (bitwp f w1 (eq_rect b word w2 a (eq_sym Heq))) b Heq.

Theorem wand_kill : forall sz (x : word sz), wzero sz ^& x = wzero sz.