diff --git a/sledge/lib/import/import.ml b/sledge/lib/import/import.ml
index e39d82d21..9e8f563e2 100644
--- a/sledge/lib/import/import.ml
+++ b/sledge/lib/import/import.ml
@@ -15,6 +15,7 @@ include (
           with module Option := Base.Option
            and module List := Base.List
            and module Set := Base.Set
+           and module Map := Base.Map
           (* prematurely deprecated, remove and use Stdlib instead *)
            and module Filename := Base.Filename
            and module Format := Base.Format
@@ -118,198 +119,8 @@ include Option.Monad_syntax
 module List = List
 module Vector = Vector
 include Vector.Infix
-
-exception Duplicate
-
 module Set = Set
-
-module Map = struct
-  module type S = sig
-    type key
-    type +'a t
-
-    val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
-    val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
-    val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
-    val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
-    val pp : key pp -> 'a pp -> 'a t pp
-
-    val pp_diff :
-         data_equal:('a -> 'a -> bool)
-      -> key pp
-      -> 'a pp
-      -> ('a * 'a) pp
-      -> ('a t * 'a t) pp
-
-    (* initial constructors *)
-    val empty : 'a t
-
-    (* constructors *)
-    val set : 'a t -> key:key -> data:'a -> 'a t
-    val add_exn : 'a t -> key:key -> data:'a -> 'a t
-    val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
-    val remove : 'a t -> key -> 'a t
-    val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
-
-    val merge :
-         'a t
-      -> 'b t
-      -> f:
-           (   key:key
-            -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
-            -> 'c option)
-      -> 'c t
-
-    val merge_skewed :
-      'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
-
-    val map : 'a t -> f:('a -> 'b) -> 'b t
-    val filter_keys : 'a t -> f:(key -> bool) -> 'a t
-    val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
-
-    (* queries *)
-    val is_empty : 'b t -> bool
-    val length : 'b t -> int
-    val mem : 'a t -> key -> bool
-    val find : 'a t -> key -> 'a option
-    val find_and_remove : 'a t -> key -> ('a * 'a t) option
-    val find_multi : 'a list t -> key -> 'a list
-    val data : 'a t -> 'a list
-    val to_alist : 'a t -> (key * 'a) list
-
-    (* traversals *)
-    val iter : 'a t -> f:('a -> unit) -> unit
-    val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
-    val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
-    val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
-  end
-
-  module Make (Key : OrderedType) : S with type key = Key.t = struct
-    module M = Caml.Map.Make (Key)
-
-    type key = Key.t
-    type 'a t = 'a M.t
-
-    let compare = M.compare
-    let equal = M.equal
-
-    let sexp_of_t sexp_of_val m =
-      List.sexp_of_t
-        (Sexplib.Conv.sexp_of_pair Key.sexp_of_t sexp_of_val)
-        (M.bindings m)
-
-    let t_of_sexp key_of_sexp val_of_sexp sexp =
-      Caml.List.fold_left
-        (fun m (k, v) -> M.add k v m)
-        M.empty
-        (List.t_of_sexp
-           (Sexplib.Conv.pair_of_sexp key_of_sexp val_of_sexp)
-           sexp)
-
-    let pp pp_k pp_v fs m =
-      Format.fprintf fs "@[<1>[%a]@]"
-        (List.pp ",@ " (fun fs (k, v) ->
-             Format.fprintf fs "@[%a @<2>↦ %a@]" pp_k k pp_v v ))
-        (M.bindings m)
-
-    let pp_diff ~data_equal pp_key pp_val pp_diff_val fs (x, y) =
-      let pp_diff_val fs = function
-        | k, `Left v ->
-            Format.fprintf fs "-- [@[%a@ @<2>↦ %a@]]" pp_key k pp_val v
-        | k, `Right v ->
-            Format.fprintf fs "++ [@[%a@ @<2>↦ %a@]]" pp_key k pp_val v
-        | k, `Unequal vv ->
-            Format.fprintf fs "[@[%a@ @<2>↦ %a@]]" pp_key k pp_diff_val vv
-      in
-      let sd =
-        M.merge
-          (fun _ v1o v2o ->
-            match (v1o, v2o) with
-            | Some v1, Some v2 when not (data_equal v1 v2) ->
-                Some (`Unequal (v1, v2))
-            | Some v1, None -> Some (`Left v1)
-            | None, Some v2 -> Some (`Right v2)
-            | _ -> None )
-          x y
-      in
-      if not (M.is_empty sd) then
-        Format.fprintf fs "[@[<hv>%a@]];@ "
-          (List.pp ";@ " pp_diff_val)
-          (M.bindings sd)
-
-    exception Duplicate
-
-    let empty = M.empty
-    let set m ~key ~data = M.add key data m
-
-    let add_exn m ~key ~data =
-      M.update key
-        (function None -> Some data | Some _ -> raise Duplicate)
-        m
-
-    let add_multi m ~key ~data =
-      M.update key
-        (function None -> Some [data] | Some vs -> Some (data :: vs))
-        m
-
-    let remove m k = M.remove k m
-    let update m k ~f = M.update k (fun vo -> Some (f vo)) m
-
-    let merge m n ~f =
-      M.merge
-        (fun k v1o v2o ->
-          match (v1o, v2o) with
-          | Some v1, Some v2 -> f ~key:k (`Both (v1, v2))
-          | Some v1, None -> f ~key:k (`Left v1)
-          | None, Some v2 -> f ~key:k (`Right v2)
-          | None, None -> None )
-        m n
-
-    let merge_skewed m n ~combine =
-      M.merge
-        (fun k v1o v2o ->
-          match (v1o, v2o) with
-          | Some v1, Some v2 -> Some (combine ~key:k v1 v2)
-          | Some _, None -> v1o
-          | None, Some _ -> v2o
-          | None, None -> None )
-        m n
-
-    let map m ~f = M.map f m
-    let filter_keys m ~f = M.filter (fun k _ -> f k) m
-
-    let filter_mapi m ~f =
-      M.fold
-        (fun k v m ->
-          match f ~key:k ~data:v with Some v' -> M.add k v' m | None -> m )
-        m M.empty
-
-    let is_empty = M.is_empty
-    let length = M.cardinal
-    let mem m k = M.mem k m
-    let find m k = M.find_opt k m
-
-    let find_and_remove m k =
-      let found = ref None in
-      let m =
-        M.update k
-          (fun v ->
-            found := v ;
-            None )
-          m
-      in
-      let+ v = !found in
-      (v, m)
-
-    let find_multi m k = try M.find k m with Not_found -> []
-    let data m = M.fold (fun _ v s -> v :: s) m []
-    let to_alist = M.bindings
-    let iter m ~f = M.iter (fun _ v -> f v) m
-    let iteri m ~f = M.iter (fun k v -> f ~key:k ~data:v) m
-    let for_alli m ~f = M.for_all (fun key data -> f ~key ~data) m
-    let fold m ~init ~f = M.fold (fun key data s -> f ~key ~data s) m init
-  end
-end
+module Map = Map
 
 module Qset = struct
   include Qset
diff --git a/sledge/lib/import/import.mli b/sledge/lib/import/import.mli
index e105c84d6..cef8f6339 100644
--- a/sledge/lib/import/import.mli
+++ b/sledge/lib/import/import.mli
@@ -15,6 +15,7 @@ include module type of (
           with module Option := Base.Option
            and module List := Base.List
            and module Set := Base.Set
+           and module Map := Base.Map
           (* prematurely deprecated, remove and use Stdlib instead *)
            and module Filename := Base.Filename
            and module Format := Base.Format
@@ -111,74 +112,8 @@ include module type of Option.Monad_syntax with type 'a t = 'a option
 module List = List
 module Vector = Vector
 include module type of Vector.Infix
-
-exception Duplicate
-
 module Set = Set
-
-module Map : sig
-  module type S = sig
-    type key
-    type +'a t
-
-    val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
-    val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
-    val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
-    val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
-    val pp : key pp -> 'a pp -> 'a t pp
-
-    val pp_diff :
-         data_equal:('a -> 'a -> bool)
-      -> key pp
-      -> 'a pp
-      -> ('a * 'a) pp
-      -> ('a t * 'a t) pp
-
-    (* initial constructors *)
-    val empty : 'a t
-
-    (* constructors *)
-    val set : 'a t -> key:key -> data:'a -> 'a t
-    val add_exn : 'a t -> key:key -> data:'a -> 'a t
-    val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
-    val remove : 'a t -> key -> 'a t
-    val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
-
-    val merge :
-         'a t
-      -> 'b t
-      -> f:
-           (   key:key
-            -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
-            -> 'c option)
-      -> 'c t
-
-    val merge_skewed :
-      'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
-
-    val map : 'a t -> f:('a -> 'b) -> 'b t
-    val filter_keys : 'a t -> f:(key -> bool) -> 'a t
-    val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
-
-    (* queries *)
-    val is_empty : 'b t -> bool
-    val length : 'b t -> int
-    val mem : 'a t -> key -> bool
-    val find : 'a t -> key -> 'a option
-    val find_and_remove : 'a t -> key -> ('a * 'a t) option
-    val find_multi : 'a list t -> key -> 'a list
-    val data : 'a t -> 'a list
-    val to_alist : 'a t -> (key * 'a) list
-
-    (* traversals *)
-    val iter : 'a t -> f:('a -> unit) -> unit
-    val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
-    val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
-    val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
-  end
-
-  module Make (Key : OrderedType) : S with type key = Key.t
-end
+module Map = Map
 
 module Qset : sig
   include module type of Qset
diff --git a/sledge/lib/import/import0.ml b/sledge/lib/import/import0.ml
index de0481cda..1bd3a0a41 100644
--- a/sledge/lib/import/import0.ml
+++ b/sledge/lib/import/import0.ml
@@ -33,3 +33,5 @@ module type OrderedType = sig
   val compare : t -> t -> int
   val sexp_of_t : t -> Sexp.t
 end
+
+exception Duplicate
diff --git a/sledge/lib/import/map.ml b/sledge/lib/import/map.ml
new file mode 100644
index 000000000..415b00fb6
--- /dev/null
+++ b/sledge/lib/import/map.ml
@@ -0,0 +1,191 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+open Import0
+
+module type S = sig
+  type key
+  type +'a t
+
+  val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
+  val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
+  val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
+  val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
+  val pp : key pp -> 'a pp -> 'a t pp
+
+  val pp_diff :
+       data_equal:('a -> 'a -> bool)
+    -> key pp
+    -> 'a pp
+    -> ('a * 'a) pp
+    -> ('a t * 'a t) pp
+
+  (* initial constructors *)
+  val empty : 'a t
+
+  (* constructors *)
+  val set : 'a t -> key:key -> data:'a -> 'a t
+  val add_exn : 'a t -> key:key -> data:'a -> 'a t
+  val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
+  val remove : 'a t -> key -> 'a t
+  val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
+
+  val merge :
+       'a t
+    -> 'b t
+    -> f:
+         (   key:key
+          -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
+          -> 'c option)
+    -> 'c t
+
+  val merge_skewed :
+    'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
+
+  val map : 'a t -> f:('a -> 'b) -> 'b t
+  val filter_keys : 'a t -> f:(key -> bool) -> 'a t
+  val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
+
+  (* queries *)
+  val is_empty : 'b t -> bool
+  val length : 'b t -> int
+  val mem : 'a t -> key -> bool
+  val find : 'a t -> key -> 'a option
+  val find_and_remove : 'a t -> key -> ('a * 'a t) option
+  val find_multi : 'a list t -> key -> 'a list
+  val data : 'a t -> 'a list
+  val to_alist : 'a t -> (key * 'a) list
+
+  (* traversals *)
+  val iter : 'a t -> f:('a -> unit) -> unit
+  val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
+  val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
+  val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
+end
+
+module Make (Key : OrderedType) : S with type key = Key.t = struct
+  module M = Stdlib.Map.Make (Key)
+
+  type key = Key.t
+  type 'a t = 'a M.t
+
+  let compare = M.compare
+  let equal = M.equal
+
+  let sexp_of_t sexp_of_val m =
+    List.sexp_of_t
+      (Sexplib.Conv.sexp_of_pair Key.sexp_of_t sexp_of_val)
+      (M.bindings m)
+
+  let t_of_sexp key_of_sexp val_of_sexp sexp =
+    List.fold_left
+      ~f:(fun m (k, v) -> M.add k v m)
+      ~init:M.empty
+      (List.t_of_sexp
+         (Sexplib.Conv.pair_of_sexp key_of_sexp val_of_sexp)
+         sexp)
+
+  let pp pp_k pp_v fs m =
+    Format.fprintf fs "@[<1>[%a]@]"
+      (List.pp ",@ " (fun fs (k, v) ->
+           Format.fprintf fs "@[%a @<2>↦ %a@]" pp_k k pp_v v ))
+      (M.bindings m)
+
+  let pp_diff ~data_equal pp_key pp_val pp_diff_val fs (x, y) =
+    let pp_diff_val fs = function
+      | k, `Left v ->
+          Format.fprintf fs "-- [@[%a@ @<2>↦ %a@]]" pp_key k pp_val v
+      | k, `Right v ->
+          Format.fprintf fs "++ [@[%a@ @<2>↦ %a@]]" pp_key k pp_val v
+      | k, `Unequal vv ->
+          Format.fprintf fs "[@[%a@ @<2>↦ %a@]]" pp_key k pp_diff_val vv
+    in
+    let sd =
+      M.merge
+        (fun _ v1o v2o ->
+          match (v1o, v2o) with
+          | Some v1, Some v2 when not (data_equal v1 v2) ->
+              Some (`Unequal (v1, v2))
+          | Some v1, None -> Some (`Left v1)
+          | None, Some v2 -> Some (`Right v2)
+          | _ -> None )
+        x y
+    in
+    if not (M.is_empty sd) then
+      Format.fprintf fs "[@[<hv>%a@]];@ "
+        (List.pp ";@ " pp_diff_val)
+        (M.bindings sd)
+
+  let empty = M.empty
+  let set m ~key ~data = M.add key data m
+
+  let add_exn m ~key ~data =
+    M.update key
+      (function None -> Some data | Some _ -> raise Duplicate)
+      m
+
+  let add_multi m ~key ~data =
+    M.update key
+      (function None -> Some [data] | Some vs -> Some (data :: vs))
+      m
+
+  let remove m k = M.remove k m
+  let update m k ~f = M.update k (fun vo -> Some (f vo)) m
+
+  let merge m n ~f =
+    M.merge
+      (fun k v1o v2o ->
+        match (v1o, v2o) with
+        | Some v1, Some v2 -> f ~key:k (`Both (v1, v2))
+        | Some v1, None -> f ~key:k (`Left v1)
+        | None, Some v2 -> f ~key:k (`Right v2)
+        | None, None -> None )
+      m n
+
+  let merge_skewed m n ~combine =
+    M.merge
+      (fun k v1o v2o ->
+        match (v1o, v2o) with
+        | Some v1, Some v2 -> Some (combine ~key:k v1 v2)
+        | Some _, None -> v1o
+        | None, Some _ -> v2o
+        | None, None -> None )
+      m n
+
+  let map m ~f = M.map f m
+  let filter_keys m ~f = M.filter (fun k _ -> f k) m
+
+  let filter_mapi m ~f =
+    M.fold
+      (fun k v m ->
+        match f ~key:k ~data:v with Some v' -> M.add k v' m | None -> m )
+      m M.empty
+
+  let is_empty = M.is_empty
+  let length = M.cardinal
+  let mem m k = M.mem k m
+  let find m k = M.find_opt k m
+
+  let find_and_remove m k =
+    let found = ref None in
+    let m =
+      M.update k
+        (fun v ->
+          found := v ;
+          None )
+        m
+    in
+    Option.map ~f:(fun v -> (v, m)) !found
+
+  let find_multi m k = try M.find k m with Not_found -> []
+  let data m = M.fold (fun _ v s -> v :: s) m []
+  let to_alist = M.bindings
+  let iter m ~f = M.iter (fun _ v -> f v) m
+  let iteri m ~f = M.iter (fun k v -> f ~key:k ~data:v) m
+  let for_alli m ~f = M.for_all (fun key data -> f ~key ~data) m
+  let fold m ~init ~f = M.fold (fun key data s -> f ~key ~data s) m init
+end
diff --git a/sledge/lib/import/map.mli b/sledge/lib/import/map.mli
new file mode 100644
index 000000000..a64666233
--- /dev/null
+++ b/sledge/lib/import/map.mli
@@ -0,0 +1,70 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+open Import0
+
+module type S = sig
+  type key
+  type +'a t
+
+  val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
+  val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
+  val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
+  val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
+  val pp : key pp -> 'a pp -> 'a t pp
+
+  val pp_diff :
+       data_equal:('a -> 'a -> bool)
+    -> key pp
+    -> 'a pp
+    -> ('a * 'a) pp
+    -> ('a t * 'a t) pp
+
+  (* initial constructors *)
+  val empty : 'a t
+
+  (* constructors *)
+  val set : 'a t -> key:key -> data:'a -> 'a t
+  val add_exn : 'a t -> key:key -> data:'a -> 'a t
+  val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
+  val remove : 'a t -> key -> 'a t
+  val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
+
+  val merge :
+       'a t
+    -> 'b t
+    -> f:
+         (   key:key
+          -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
+          -> 'c option)
+    -> 'c t
+
+  val merge_skewed :
+    'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
+
+  val map : 'a t -> f:('a -> 'b) -> 'b t
+  val filter_keys : 'a t -> f:(key -> bool) -> 'a t
+  val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
+
+  (* queries *)
+  val is_empty : 'b t -> bool
+  val length : 'b t -> int
+  val mem : 'a t -> key -> bool
+  val find : 'a t -> key -> 'a option
+  val find_and_remove : 'a t -> key -> ('a * 'a t) option
+  val find_multi : 'a list t -> key -> 'a list
+  val data : 'a t -> 'a list
+  val to_alist : 'a t -> (key * 'a) list
+
+  (* traversals *)
+  val iter : 'a t -> f:('a -> unit) -> unit
+  val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
+  val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
+  val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
+end
+
+module Make (Key : OrderedType) : S with type key = Key.t