Section MoreLemmas.
Context {A val : Type} {Heq : RelDec (@eq A)} {HeqOk : RelDec_Correct Heq}.
Context {R : ValNull val}.
Open Scope open_scope.
Definition subst_substlist (es fs : @substlist A val) : substlist :=
map (fun x => (fst x, (snd x) // fs)) es.

Lemma subst_combine {B} (e : @open A val B) (es fs : substlist) :
(e // es // fs) = (e // (app (subst_substlist es fs) fs)).