diff --git a/src/core/internal.ml b/src/core/internal.ml
index b7050eb6..a33d3f7c 100644
--- a/src/core/internal.ml
+++ b/src/core/internal.ml
@@ -255,8 +255,8 @@ module Make
      its subterms.
   *)
   let insert_var_order = function
-    | Either.Left l -> Iheap.insert f_weight env.order l.lid
-    | Either.Right v ->
+    | E_lit l -> Iheap.insert f_weight env.order l.lid
+    | E_var v ->
       Iheap.insert f_weight env.order v.vid;
       iter_sub (fun t -> Iheap.insert f_weight env.order t.lid) v
 
@@ -456,12 +456,12 @@ module Make
         match (Vec.get env.elt_queue c) with
         (* A literal is unassigned, we nedd to add it back to
            the heap of potentially assignable literals. *)
-        | Either.Left l ->
+        | Lit l ->
           l.assigned <- None;
           l.l_level <- -1;
           insert_var_order (elt_of_lit l)
         (* A variable is not true/false anymore, one of two things can happen: *)
-        | Either.Right a ->
+        | Atom a ->
           if a.var.v_level <= lvl then begin
             (* It is a semantic propagation, which can be late, and has a level
                lower than where we backtrack, so we just move it to the head
@@ -594,8 +594,8 @@ module Make
           decr tr_ind;
           Log.debugf 20 "Looking at trail element %d" (fun k->k !tr_ind);
           match Vec.get env.elt_queue !tr_ind with
-          | Either.Left _ -> ()
-          | Either.Right a ->
+          | Lit _ -> ()
+          | Atom a ->
             begin match a.var.reason with
               | Some (Bcp d) ->
                 let tmp, res = Proof.resolve (Proof.merge !c (Proof.to_list d)) in
@@ -619,7 +619,7 @@ module Make
 
   let get_atom i =
     match Vec.get env.elt_queue i with
-    | Either.Left _ -> assert false | Either.Right x -> x
+    | Lit _ -> assert false | Atom x -> x
 
   let analyze_sat c_clause =
     let pathC  = ref 0 in
@@ -829,11 +829,11 @@ module Make
 
   let slice_get i =
     match Vec.get env.elt_queue i with
-    | Either.Right a ->
+    | Atom a ->
       Plugin_intf.Lit a.lit
-    | Either.Left {l_level; term; assigned = Some v} ->
+    | Lit {l_level; term; assigned = Some v} ->
       Plugin_intf.Assign (term, v, l_level)
-    | Either.Left _ -> assert false
+    | Lit _ -> assert false
 
   let slice_push l lemma =
     let atoms = List.rev_map (fun x -> new_atom x) l in
@@ -900,8 +900,8 @@ module Make
       let res = ref None in
       while env.elt_head < Vec.size env.elt_queue do
         begin match Vec.get env.elt_queue env.elt_head with
-          | Either.Left _ -> ()
-          | Either.Right a ->
+          | Lit _ -> ()
+          | Atom a ->
             incr num_props;
             propagate_atom a res
         end;
@@ -1011,7 +1011,7 @@ module Make
     | None ->
       begin try
           begin match St.get_elt (Iheap.remove_min f_weight env.order) with
-            | Either.Left l ->
+            | E_lit l ->
               if l.l_level >= 0 then
                 pick_branch_lit ()
               else begin
@@ -1021,7 +1021,7 @@ module Make
                 let current_level = decision_level () in
                 enqueue_assign l value current_level
               end
-            | Either.Right v ->
+            | E_var v ->
               pick_branch_aux v.pa
           end
         with Not_found -> raise Sat
@@ -1142,8 +1142,8 @@ module Make
   let model () =
     let opt = function Some a -> a | None -> assert false in
     Vec.fold (fun acc e -> match e with
-        | Either.Left v -> (v.term, opt v.assigned)  :: acc
-        | Either.Right _ -> acc
+        | Lit v -> (v.term, opt v.assigned)  :: acc
+        | Atom _ -> acc
       ) [] env.elt_queue
 
   (* Backtrack to decision_level 0, with trail_lim && theory env specified *)
@@ -1153,11 +1153,11 @@ module Make
     env.elt_head <- elt_lvl;
     for c = env.elt_head to Vec.size env.elt_queue - 1 do
       match Vec.get env.elt_queue c with
-      | Either.Left l ->
+      | Lit l ->
         l.assigned <- None;
         l.l_level <- -1;
         insert_var_order (elt_of_lit l)
-      | Either.Right a ->
+      | Atom a ->
         begin match a.var.reason with
           | Some Bcp { c_level } when c_level > push_lvl ->
             a.is_true <- false;
@@ -1210,8 +1210,8 @@ module Make
                  (if i = ul.ul_th_lvl then "*" else " ")
                  i (fun fmt e ->
                      match e with
-                     | Either.Left l -> St.pp_lit fmt l
-                     | Either.Right a -> St.pp_atom fmt a)
+                     | Lit l -> St.pp_lit fmt l
+                     | Atom a -> St.pp_atom fmt a)
                  (Vec.get env.elt_queue i)
              done
            in
diff --git a/src/core/solver_types.ml b/src/core/solver_types.ml
index 621c2f71..b0122364 100644
--- a/src/core/solver_types.ml
+++ b/src/core/solver_types.ml
@@ -75,7 +75,9 @@ module McMake (E : Expr_intf.S)(Dummy : sig end) = struct
     | Lemma of proof
     | History of clause list
 
-  type elt = (lit, var) Either.t
+  type elt =
+    | E_lit of lit
+    | E_var of var
 
   (* Dummy values *)
   let dummy_lit = E.dummy
@@ -118,7 +120,7 @@ module McMake (E : Expr_intf.S)(Dummy : sig end) = struct
   let f_map = MF.create 4096
   let t_map = MT.create 4096
 
-  let vars = Vec.make 107 (Either.mk_right dummy_var)
+  let vars = Vec.make 107 (E_var dummy_var)
   let nb_elt () = Vec.size vars
   let get_elt i = Vec.get vars i
   let iter_elt f = Vec.iter f vars
@@ -137,7 +139,7 @@ module McMake (E : Expr_intf.S)(Dummy : sig end) = struct
       } in
       incr cpt_mk_var;
       MT.add t_map t res;
-      Vec.push vars (Either.mk_left res);
+      Vec.push vars (E_lit res);
       res
 
   let make_boolean_var : formula -> var * Expr_intf.negated =
@@ -172,7 +174,7 @@ module McMake (E : Expr_intf.S)(Dummy : sig end) = struct
             aid = cpt_fois_2 + 1 (* aid = vid*2+1 *) } in
         MF.add f_map lit var;
         incr cpt_mk_var;
-        Vec.push vars (Either.mk_right var);
+        Vec.push vars (E_var var);
         var, negated
 
   let add_term t = make_semantic_var t
@@ -203,27 +205,28 @@ module McMake (E : Expr_intf.S)(Dummy : sig end) = struct
   let empty_clause = make_clause "Empty" [] (History [])
 
   (* Decisions & propagations *)
-  type t = (lit, atom) Either.t
+  type t =
+    | Lit of lit
+    | Atom of atom
 
-  let of_lit = Either.mk_left
-  let of_atom = Either.mk_right
-  let destruct = Either.destruct
+  let of_lit l = Lit l
+  let of_atom a = Atom a
 
   (* Elements *)
-  let elt_of_lit = Either.mk_left
-  let elt_of_var = Either.mk_right
+  let elt_of_lit l = E_lit l
+  let elt_of_var v = E_var v
 
   let get_elt_id = function
-    | Either.Left l -> l.lid | Either.Right v ->  v.vid
+    | E_lit l -> l.lid | E_var v ->  v.vid
   let get_elt_level = function
-    | Either.Left l -> l.l_level | Either.Right v ->  v.v_level
+    | E_lit l -> l.l_level | E_var v ->  v.v_level
   let get_elt_weight = function
-    | Either.Left l -> l.l_weight | Either.Right v ->  v.v_weight
+    | E_lit l -> l.l_weight | E_var v ->  v.v_weight
 
   let set_elt_level e lvl = match e with
-    | Either.Left l -> l.l_level <- lvl | Either.Right v ->  v.v_level <- lvl
+    | E_lit l -> l.l_level <- lvl | E_var v ->  v.v_level <- lvl
   let set_elt_weight e w = match e with
-    | Either.Left l -> l.l_weight <- w | Either.Right v ->  v.v_weight <- w
+    | E_lit l -> l.l_weight <- w | E_var v ->  v.v_weight <- w
 
   (* Name generation *)
   let fresh_lname =
diff --git a/src/core/solver_types_intf.ml b/src/core/solver_types_intf.ml
index 30796073..66cb0544 100644
--- a/src/core/solver_types_intf.ml
+++ b/src/core/solver_types_intf.ml
@@ -71,7 +71,9 @@ module type S = sig
     | History of clause list
 
   (** {2 Decisions and propagations} *)
-  type t = (lit, atom) Either.t
+  type t =
+    | Lit of lit
+    | Atom of atom
   (** Either a lit of an atom *)
 
   val of_lit : lit -> t
@@ -80,7 +82,9 @@ module type S = sig
 
   (** {2 Elements} *)
 
-  type elt = (lit, var) Either.t
+  type elt =
+    | E_lit of lit
+    | E_var of var
   (** Either a lit of a var *)
 
   val nb_elt : unit -> int
diff --git a/src/util/either.ml b/src/util/either.ml
deleted file mode 100644
index c48c6dda..00000000
--- a/src/util/either.ml
+++ /dev/null
@@ -1,16 +0,0 @@
-(*
-MSAT is free software, using the Apache license, see file LICENSE
-Copyright 2014 Guillaume Bury
-Copyright 2014 Simon Cruanes
-*)
-
-type ('a, 'b) t =
-  | Left of 'a
-  | Right of 'b
-
-let mk_left a = Left a
-let mk_right b = Right b
-
-let destruct e f_left f_right = match e with
-  | Left a -> f_left a
-  | Right b -> f_right b
diff --git a/src/util/either.mli b/src/util/either.mli
deleted file mode 100644
index 3a90b9cf..00000000
--- a/src/util/either.mli
+++ /dev/null
@@ -1,15 +0,0 @@
-(*
-MSAT is free software, using the Apache license, see file LICENSE
-Copyright 2014 Guillaume Bury
-Copyright 2014 Simon Cruanes
-*)
-
-type ('a, 'b) t =
-  | Left of 'a
-  | Right of 'b
-
-val mk_left : 'a -> ('a, 'b) t
-val mk_right : 'b -> ('a, 'b) t
-
-val destruct : ('a, 'b) t ->
-  ('a -> 'c) -> ('b -> 'c) -> 'c