Definition setpair (p: rpair mreg) (v: val) (m: t) : t :=
match p with
| One r => set (R r) v m
| Twolong hi lo => set (R lo) (Val.loword  v) (set (R hi) (Val.hiword v) m)
end.

Lemma getpair_exten:
forall p ls1 ls2,
(forall l, In l (regs_of_rpair p) -> ls2 l = ls1 l) ->
getpair p ls2 = getpair p ls1.