diff --git a/src/data/CCIntMap.ml b/src/data/CCIntMap.ml
index af62e8a4..26fba781 100644
--- a/src/data/CCIntMap.ml
+++ b/src/data/CCIntMap.ml
@@ -17,12 +17,13 @@ module Bit : sig
   val mask : mask:t -> int -> int   (* zeroes the bit, puts all lower bits to 1 *)
   val lt : t -> t -> bool
   val gt : t -> t -> bool
+  val equal_int : int -> t -> bool
 end = struct
   type t = int
 
   let min_int = min_int
 
-  let equal = (=)
+  let equal : t -> t -> bool = Pervasives.(=)
 
   let rec highest_bit_naive x m =
     if x=m then m
@@ -33,26 +34,45 @@ end = struct
 
   let highest x =
     if x<0 then min_int
-    else if Sys.word_size > 40 && x > mask_40_
-    then (* remove least significant 40 bits *)
+    else if Sys.word_size > 40 && x > mask_40_ then (
+      (* remove least significant 40 bits *)
       let x' = x land (lnot (mask_40_ -1)) in
       highest_bit_naive x' mask_40_
-    else if x> mask_20_
-    then (* small shortcut: remove least significant 20 bits *)
+    ) else if x> mask_20_ then (
+      (* small shortcut: remove least significant 20 bits *)
       let x' = x land (lnot (mask_20_ -1)) in
       highest_bit_naive x' mask_20_
-    else highest_bit_naive x 1
+    ) else (
+      highest_bit_naive x 1
+    )
 
-  let is_0 ~bit x = x land bit = 0
-  let is_1 ~bit x = x land bit = bit
+  let[@inline] is_0 ~bit x = x land bit = 0
+  let[@inline] is_1 ~bit x = x land bit = bit
 
-  let mask ~mask x = (x lor (mask -1)) land (lnot mask)
+  let[@inline] mask ~mask x = (x lor (mask -1)) land (lnot mask)
   (* low endian: let mask_ x ~mask = x land (mask - 1) *)
 
-  let gt a b = (b != min_int) && (a = min_int || a > b)
-  let lt a b = gt b a
+  let[@inline] gt a b = (b != min_int) && (a = min_int || a > b)
+  let[@inline] lt a b = gt b a
+  let equal_int = Pervasives.(=)
 end
 
+(*$inject
+  let highest2 x : int =
+    let rec aux i =
+      if i=0 then i
+      else if 1 = (x lsr i) then 1 lsl i else aux (i-1)
+    in
+    if x<0 then min_int else aux (Sys.word_size-2)
+*)
+
+(*$QR & ~count:1_000
+  Q.int (fun x ->
+    if Bit.equal_int (highest2 x) (Bit.highest x) then true
+    else QCheck.Test.fail_reportf "x=%d, highest=%d, highest2=%d@." x
+      (Bit.highest x :> int) (highest2 x))
+  *)
+
 type 'a t =
   | E  (* empty *)
   | L of int * 'a  (* leaf *)
@@ -60,10 +80,11 @@ type 'a t =
 
 let empty = E
 
-let is_prefix_ ~prefix y ~bit = prefix = Bit.mask y ~mask:bit
+let[@inline] is_prefix_ ~prefix y ~bit =
+  prefix = Bit.mask y ~mask:bit
 
 (*$inject
-  let _list_uniq = CCList.sort_uniq ~cmp:(fun a b-> Pervasives.compare (fst a)(fst b))
+  let _list_uniq l = CCList.sort_uniq ~cmp:(fun a b-> Pervasives.compare (fst a)(fst b)) l
 *)
 
 (*$Q
@@ -92,7 +113,7 @@ let is_prefix_ ~prefix y ~bit = prefix = Bit.mask y ~mask:bit
 *)
 
 (* low endian: let branching_bit_ a _ b _ = lowest_bit_ (a lxor b) *)
-let branching_bit_ a b = Bit.highest (a lxor b)
+let[@inline] branching_bit_ a b = Bit.highest (a lxor b)
 
 (* TODO use hint in branching_bit_ *)
 
@@ -103,15 +124,14 @@ let check_invariants t =
     | L (k, _) ->
       List.for_all
         (fun (prefix, switch, side) ->
-           is_prefix_ ~prefix k ~bit:switch
-           &&
-           match side with
+           is_prefix_ ~prefix k ~bit:switch &&
+           begin match side with
              | `Left -> Bit.is_0 k ~bit:switch
              | `Right -> Bit.is_1 k ~bit:switch
-        ) path
+           end)
+        path
     | N (prefix, switch, l, r) ->
-      check_keys ((prefix, switch, `Left) :: path) l
-      &&
+      check_keys ((prefix, switch, `Left) :: path) l &&
       check_keys ((prefix, switch, `Right) :: path) r
   in
   check_keys [] t
@@ -126,11 +146,13 @@ let rec find_exn k t = match t with
   | L (k', v) when k = k' -> v
   | L _ -> raise Not_found
   | N (prefix, m, l, r) ->
-    if is_prefix_ ~prefix k ~bit:m
-    then if Bit.is_0 k ~bit:m
+    if is_prefix_ ~prefix k ~bit:m then (
+      if Bit.is_0 k ~bit:m
       then find_exn k l
       else find_exn k r
-    else raise Not_found
+    ) else (
+      raise Not_found
+    )
 
 (* XXX could test with lt_unsigned_? *)
 
@@ -161,7 +183,7 @@ let mem k t =
     List.for_all (fun (k,_) -> mem k m) l)
 *)
 
-let mk_node_ prefix switch l r = match l, r with
+let[@inline] mk_node_ prefix switch l r = match l, r with
   | E, o | o, E -> o
   | _ -> N (prefix, switch, l, r)
 
@@ -170,8 +192,7 @@ let mk_node_ prefix switch l r = match l, r with
 let join_ t1 p1 t2 p2 =
   let switch = branching_bit_ p1 p2 in
   let prefix = Bit.mask p1 ~mask:switch in
-  if Bit.is_0 p1 ~bit:switch
-  then (
+  if Bit.is_0 p1 ~bit:switch then (
     assert (Bit.is_1 p2 ~bit:switch);
     mk_node_ prefix switch t1 t2
   ) else (
@@ -179,7 +200,7 @@ let join_ t1 p1 t2 p2 =
     mk_node_ prefix switch t2 t1
   )
 
-let singleton k v = L (k, v)
+let[@inline] singleton k v = L (k, v)
 
 (* c: conflict function *)
 let rec insert_ c k v t = match t with
@@ -189,11 +210,13 @@ let rec insert_ c k v t = match t with
     then L (k, c ~old:v' v)
     else join_ t k' (L (k, v)) k
   | N (prefix, switch, l, r) ->
-    if is_prefix_ ~prefix k ~bit:switch
-    then if Bit.is_0 k ~bit:switch
+    if is_prefix_ ~prefix k ~bit:switch then (
+      if Bit.is_0 k ~bit:switch
       then N(prefix, switch, insert_ c k v l, r)
       else N(prefix, switch, l, insert_ c k v r)
-    else join_ (L(k,v)) k t prefix
+    ) else (
+      join_ (L(k,v)) k t prefix
+    )
 
 let add k v t = insert_ (fun ~old:_ v -> v) k v t
 
@@ -207,11 +230,13 @@ let rec remove k t = match t with
   | E -> E
   | L (k', _) -> if k=k' then E else t
   | N (prefix, switch, l, r) ->
-    if is_prefix_ ~prefix k ~bit:switch
-    then if Bit.is_0 k ~bit:switch
+    if is_prefix_ ~prefix k ~bit:switch then (
+      if Bit.is_0 k ~bit:switch
       then mk_node_ prefix switch (remove k l) r
       else mk_node_ prefix switch l (remove k r)
-    else t (* not present *)
+    ) else (
+      t (* not present *)
+    )
 
 (*$Q & ~count:20
   Q.(list (pair int int)) (fun l -> \
@@ -240,7 +265,9 @@ let update k f t =
 
 let doubleton k1 v1 k2 v2 = add k1 v1 (singleton k2 v2)
 
-let rec equal ~eq a b = Pervasives.(==) a b || match a, b with
+let rec equal ~eq a b =
+  Pervasives.(==) a b ||
+  begin match a, b with
     | E, E -> true
     | L (ka, va), L (kb, vb) -> ka = kb && eq va vb
     | N (pa, sa, la, ra), N (pb, sb, lb, rb) ->
@@ -248,6 +275,7 @@ let rec equal ~eq a b = Pervasives.(==) a b || match a, b with
     | E, _
     | N _, _
     | L _, _ -> false
+  end
 
 (*$Q
   Q.(list (pair int bool)) ( fun l -> \
@@ -289,26 +317,29 @@ let choose t =
   try Some (choose_exn t)
   with Not_found -> None
 
+(** {2 Whole-collection operations} *)
+
 let rec union f t1 t2 =
-  if Pervasives.(==) t1 t2 then t1
-  else match t1, t2 with
+  match t1, t2 with
     | E, o | o, E -> o
     | L (k, v), o
     | o, L (k, v) ->
       (* insert k, v into o *)
       insert_ (fun ~old v -> f k old v) k v o
     | N (p1, m1, l1, r1), N (p2, m2, l2, r2) ->
-      if p1 = p2 && Bit.equal m1 m2
-      then mk_node_ p1 m1 (union f l1 l2) (union f r1 r2)
-      else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1
-      then if Bit.is_0 p2 ~bit:m1
+      if p1 = p2 && Bit.equal m1 m2 then (
+        mk_node_ p1 m1 (union f l1 l2) (union f r1 r2)
+      ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
+        if Bit.is_0 p2 ~bit:m1
         then N (p1, m1, union f l1 t2, r1)
         else N (p1, m1, l1, union f r1 t2)
-      else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2
-      then if Bit.is_0 p1 ~bit:m2
+      ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
+        if Bit.is_0 p1 ~bit:m2
         then N (p2, m2, union f t1 l2, r2)
         else N (p2, m2, l2, union f t1 r2)
-      else join_ t1 p1 t2 p2
+      ) else (
+        join_ t1 p1 t2 p2
+      )
 
 (*$Q & ~small:(fun (a,b) -> List.length a + List.length b)
   Q.(pair (list (pair int bool)) (list (pair int bool))) (fun (l1,l2) -> \
@@ -344,9 +375,30 @@ let rec union f t1 t2 =
     equal ~eq:(=) (of_list l) (union (fun _ a _ -> a) (of_list l)(of_list l)))
 *)
 
+(*$inject
+  let union_l l1 l2 =
+    let l2' = List.filter (fun (x,_) -> not @@ List.mem_assoc x l1) l2 in
+    _list_uniq (l1 @ l2')
+
+  let inter_l l1 l2 =
+    let l2' = List.filter (fun (x,_) -> List.mem_assoc x l1) l2 in
+    _list_uniq l2'
+*)
+
+(*$QR
+  Q.(pair (small_list (pair small_int unit)) (small_list (pair small_int unit)))
+    (fun (l1,l2) ->
+      union_l l1 l2 = _list_uniq @@ to_list (union (fun _ _ _ ->())(of_list l1) (of_list l2)))
+  *)
+
+(*$QR
+  Q.(pair (small_list (pair small_int unit)) (small_list (pair small_int unit)))
+    (fun (l1,l2) ->
+      inter_l l1 l2 = _list_uniq @@ to_list (inter (fun _ _ _ ->()) (of_list l1) (of_list l2)))
+  *)
+
 let rec inter f a b =
-  if Pervasives.(==) a b then a
-  else match a, b with
+  match a, b with
     | E, _ | _, E -> E
     | L (k, v), o
     | o, L (k, v) ->
@@ -356,17 +408,17 @@ let rec inter f a b =
         with Not_found -> E
       end
     | N (p1, m1, l1, r1), N (p2, m2, l2, r2) ->
-      if p1 = p2 && Bit.equal m1 m2
-      then mk_node_ p1 m1 (inter f l1 l2) (inter f r1 r2)
-      else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1
-      then if Bit.is_0 p2 ~bit:m1
+      if p1 = p2 && Bit.equal m1 m2 then (
+        mk_node_ p1 m1 (inter f l1 l2) (inter f r1 r2)
+      ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
+        if Bit.is_0 p2 ~bit:m1
         then inter f l1 b
         else inter f r1 b
-      else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2
-      then if Bit.is_0 p1 ~bit:m2
+      ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
+        if Bit.is_0 p1 ~bit:m2
         then inter f a l2
         else inter f a r2
-      else E
+      ) else E
 
 (*$R
   assert_equal ~cmp:(equal ~eq:(=)) ~printer:(CCFormat.to_string (pp CCString.pp))
@@ -465,11 +517,12 @@ let compare ~cmp a b =
     | Some _, None -> 1
     | None, Some _ -> -1
     | Some (ka, va), Some (kb, vb) ->
-      if ka=kb
-      then
+      if ka=kb then (
         let c = cmp va vb in
         if c=0 then cmp_gen cmp a b else c
-      else compare ka kb
+      ) else (
+        compare ka kb
+      )
   in
   cmp_gen cmp (to_gen a) (to_gen b)
 
diff --git a/src/data/CCIntMap.mli b/src/data/CCIntMap.mli
index 2036ddb9..04874954 100644
--- a/src/data/CCIntMap.mli
+++ b/src/data/CCIntMap.mli
@@ -118,6 +118,7 @@ module Bit : sig
   type t = private int
   val min_int : t
   val highest : int -> t
+  val equal_int : int -> t -> bool
 end
 val check_invariants : _ t -> bool