+(* This is the inverse of the subst function. *)
+let subst_inv ~equality ~what =
+ let rec find_image t = function
+ | [] -> false
+ | hd :: tl -> equality t hd || find_image t tl
+ in
+ let rec subst_term k t =
+ if find_image t what then C.Rel k else inspect_term k t
+ and inspect_term k = function
+ | C.Rel n -> if n < k then C.Rel n else C.Rel (succ n)
+ | C.Sort _ as t -> t
+ | C.Implicit _ as t -> t
+ | C.Var (uri, enss) ->
+ let enss = List.map (subst_ens k) enss in
+ C.Var (uri, enss)
+ | C.Const (uri ,enss) ->
+ let enss = List.map (subst_ens k) enss in
+ C.Const (uri, enss)
+ | C.MutInd (uri, tyno, enss) ->
+ let enss = List.map (subst_ens k) enss in
+ C.MutInd (uri, tyno, enss)
+ | C.MutConstruct (uri, tyno, consno, enss) ->
+ let enss = List.map (subst_ens k) enss in
+ C.MutConstruct (uri, tyno, consno, enss)
+ | C.Meta (i, mss) ->
+ let mss = List.map (subst_ms k) mss in
+ C.Meta(i, mss)
+ | C.Cast (t, v) -> C.Cast (subst_term k t, subst_term k v)
+ | C.Appl ts ->
+ let ts = List.map (subst_term k) ts in
+ C.Appl ts
+ | C.MutCase (uri, tyno, outty, t, cases) ->
+ let cases = List.map (subst_term k) cases in
+ C.MutCase (uri, tyno, subst_term k outty, subst_term k t, cases)
+ | C.Prod (n, v, t) ->
+ C.Prod (n, subst_term k v, subst_term (succ k) t)
+ | C.Lambda (n, v, t) ->
+ C.Lambda (n, subst_term k v, subst_term (succ k) t)
+ | C.LetIn (n, v, t) ->
+ C.LetIn (n, subst_term k v, subst_term (succ k) t)
+ | C.Fix (i, fixes) ->
+ let fixesno = List.length fixes in
+ let fixes = List.map (subst_fix fixesno k) fixes in
+ C.Fix (i, fixes)
+ | C.CoFix (i, cofixes) ->
+ let cofixesno = List.length cofixes in
+ let cofixes = List.map (subst_cofix cofixesno k) cofixes in
+ C.CoFix (i, cofixes)
+ and subst_ens k (uri, t) = uri, subst_term k t
+ and subst_ms k = function
+ | None -> None
+ | Some t -> Some (subst_term k t)
+ and subst_fix fixesno k (n, ind, ty, bo) =
+ n, ind, subst_term k ty, subst_term (k + fixesno) bo
+ and subst_cofix cofixesno k (n, ty, bo) =
+ n, subst_term k ty, subst_term (k + cofixesno) bo
+in
+subst_term
+
+
+
+