+let subst_tac ~hyp =
+ let hole = C.Implicit (Some `Hole) in
+ let map self = function
+ | Some (C.Name s, _) when s <> self -> Some (s, hole)
+ | _ -> None
+ in
+ let subst_tac status =
+ let (proof, goal) = status in
+ let (_, metasenv, _, _) = proof in
+ let _, context, _ = CicUtil.lookup_meta goal metasenv in
+ let what = match PEH.get_rel context hyp with
+ | Some t -> t
+ | None -> raise (PET.Fail msg0)
+ in
+ let ty, _ = TC.type_of_aux' metasenv context what CicUniv.empty_ugraph in
+ let direction, i, t = match ty with
+ | (C.Appl [(C.MutInd (uri, 0, [])); _; C.Rel i; t])
+ when LO.is_eq_URI uri -> `LeftToRight, i, t
+ | (C.Appl [(C.MutInd (uri, 0, [])); _; t; C.Rel i])
+ when LO.is_eq_URI uri -> `RightToLeft, i, t
+ | _ -> raise (PET.Fail msg1)
+ in
+ let var = match PEH.get_name context i with
+ | Some name -> name
+ | None -> raise (PET.Fail msg0)
+ in
+ if DTI.does_not_occur i t then () else raise (PET.Fail msg2);
+ let pattern = None, PEH.list_rev_map_filter (map hyp) context, Some hole in
+ let start = rewrite_tac ~direction ~pattern what in
+ let continuation = PESR.clear ~hyps:[hyp; var] in
+ let tac = T.then_ ~start ~continuation in
+ PET.apply_tactic tac status
+ in
+ PET.mk_tactic subst_tac