-let delift metasenv subst context n l t =
- let rec aux k (metasenv, subst as ms) = function
+let delift ~unify metasenv subst context n l t =
+ let unify_list in_scope =
+ match l with
+ | _, NCic.Irl _ -> fun _ _ _ _ _ -> None
+ | shift, NCic.Ctx l -> fun metasenv subst context k t ->
+ if flexible_arg subst t then None else
+ let lb = List.map (fun t -> t, flexible_arg subst t) l in
+ HExtlib.list_findopt
+ (fun (li,flexible) i ->
+ if flexible || i < in_scope then None else
+ let li = NCicSubstitution.lift (k+shift) li in
+ match unify metasenv subst context li t with
+ | Some (metasenv,subst) ->
+ Some ((metasenv, subst), NCic.Rel (i+1+k))
+ | None -> None)
+ lb
+ in
+ let rec aux (context,k,in_scope) (metasenv, subst as ms) t =
+ match unify_list in_scope metasenv subst context k t with
+ | Some x -> x
+ | None ->
+ match t with