Ltac wlt_ind :=
match goal with
| [ |- forall (n: word ?len), ?P ] =>
refine (well_founded_ind (@wlt_wf len) (fun n => P) _)
end.

Theorem wordToNat_plusone: forall sz w w', w < w' ->
wordToNat (w ^+ natToWord sz 1) = S (wordToNat w).