Section Properties.
Context {A val : Type} {Heq : RelDec (@eq A)} {HeqOk : RelDec_Correct Heq}.
Context {R : ValNull val}.

Lemma open_subst_stack {B} (m: @open A val B) (sub : subst) (s : @stack A val) :
(apply_subst m sub) s = m (stack_subst s sub).