let term' = reduction context term in
(* We don't know if [term] is a subterm of [ty] or a subterm of *)
(* the type of one metavariable. So we replace it everywhere. *)
let term' = reduction context term in
(* We don't know if [term] is a subterm of [ty] or a subterm of *)
(* the type of one metavariable. So we replace it everywhere. *)