Inductive contextlist' : (exprlist -> expr) -> Prop :=
| contextlist'_call: forall r1 rl0 ty C,
context RV RV C ->
contextlist' (fun rl => C (Ecall r1 (exprlist_app rl0 rl) ty))
| contextlist'_builtin: forall ef tyargs rl0 ty C,
context RV RV C ->
contextlist' (fun rl => C (Ebuiltin ef tyargs (exprlist_app rl0 rl) ty)).

Lemma contextlist'_head:
forall rl C,
contextlist' C ->
context RV RV (fun x => C (Econs x rl)).