Hint Resolve word_neq lt_le eq_le sub_0_eq le_neq_lt : worder.
Ltac shatter_word x :=
match type of x with
| word 0 => try rewrite (shatter_word_0 x) in *
| word (S ?N) =>
let x' := fresh in
let H := fresh in
destruct (@shatter_word_S N x) as [ ? [ x' H ] ];
rewrite H in *; clear H; shatter_word x'
end.

(* Specifications: *)
(** Uniqueness of equality proofs **)
Lemma rewrite_weq : forall sz (a b : word sz)
(pf : a = b),
weq a b = left _ pf.