Hint Resolve agree_reg agree_reglist: stacking.
(** Preservation under assignments of machine registers. *)

Lemma agree_regs_exten:
forall j ls rs ls' rs',
agree_regs j ls rs ->
(forall r, ls' (R r) = Vundef \/ ls' (R r) = ls (R r) /\ rs' r = rs r) ->
agree_regs j ls' rs'.