diff --git a/serlib/ser_constr.ml b/serlib/ser_constr.ml
index 69b2077..47fa06a 100644
--- a/serlib/ser_constr.ml
+++ b/serlib/ser_constr.ml
@@ -99,11 +99,13 @@ type 'constr pcase_branch =
 let map_pcase_branch f (bi, c) = (bi, f c)
 
 type 'types pcase_return =
-  [%import: 'constr Constr.pcase_return]
+  [%import: 'types Constr.pcase_return]
   [@@deriving sexp,yojson]
 
 let map_pcase_return f (bi, c) = (bi, f c)
 
+type 'a identity = 'a [@@deriving sexp,yojson]
+
 type _constr =
   | Rel       of int
   | Var       of Names.Id.t
@@ -126,7 +128,7 @@ type _constr =
   | Float     of Float64.t
   | Array     of Univ.Instance.t * _constr array * _constr * _types
 [@@deriving sexp,yojson]
-and _types = _constr
+and _types = _constr identity
 [@@deriving sexp,yojson]
 
 let rec _constr_put (c : constr) : _constr =
diff --git a/serlib/ser_locus.ml b/serlib/ser_locus.ml
index 1f74ebc..cdcfc99 100644
--- a/serlib/ser_locus.ml
+++ b/serlib/ser_locus.ml
@@ -57,7 +57,7 @@ type clause_atom =
   [%import: Locus.clause_atom]
   [@@deriving sexp]
 
-type concrete_clause =
+type 'id concrete_clause =
   [%import: 'id Locus.clause_expr]
   [@@deriving sexp]
 
@@ -65,7 +65,7 @@ type hyp_location =
   [%import: Locus.clause_atom]
   [@@deriving sexp]
 
-type goal_location =
+type 'id goal_location =
   [%import: 'id Locus.clause_expr]
   [@@deriving sexp]
 
@@ -73,7 +73,7 @@ type simple_clause =
   [%import: Locus.clause_atom]
   [@@deriving sexp]
 
-type 'a or_like_first =
+type 'id or_like_first =
   [%import: 'id Locus.clause_expr]
   [@@deriving sexp]
 
diff --git a/serlib/ser_stdlib.ml b/serlib/ser_stdlib.ml
index fdb1720..3907548 100644
--- a/serlib/ser_stdlib.ml
+++ b/serlib/ser_stdlib.ml
@@ -16,6 +16,16 @@
 open Sexplib.Conv
 
 type nonrec 'a ref = 'a ref
+let ref = ref
+let ( ! ) = ( ! )
+let ( := ) = ( := )
+
+module Option = struct
+  type 'a t = 'a option =
+    | None
+    | Some of 'a
+  [@@deriving sexp]
+end
 
 let ref_of_sexp = ref_of_sexp
 let sexp_of_ref = sexp_of_ref