diff --git a/sledge/nonstdlib/array.ml b/sledge/nonstdlib/array.ml
index afc97c784..498d92fba 100644
--- a/sledge/nonstdlib/array.ml
+++ b/sledge/nonstdlib/array.ml
@@ -69,6 +69,7 @@ let combine_exn xs ys =
 let combine xs ys =
   try Some (combine_exn xs ys) with Invalid_argument _ -> None
 
+let mem x xs ~eq = mem ~eq x xs
 let iter xs ~f = iter ~f xs
 let iteri xs ~f = iteri ~f xs
 let exists xs ~f = exists ~f xs
diff --git a/sledge/nonstdlib/array.mli b/sledge/nonstdlib/array.mli
index a62e3136d..66d4effba 100644
--- a/sledge/nonstdlib/array.mli
+++ b/sledge/nonstdlib/array.mli
@@ -23,6 +23,7 @@ val split : ('a * 'b) t -> 'a t * 'b t
 val combine : 'a t -> 'b t -> ('a * 'b) t option
 val combine_exn : 'a t -> 'b t -> ('a * 'b) t
 val is_empty : 'a t -> bool
+val mem : 'a -> 'a t -> eq:('a -> 'a -> bool) -> bool
 val iter : 'a t -> f:('a -> unit) -> unit
 val iteri : 'a t -> f:(int -> 'a -> unit) -> unit
 val exists : 'a t -> f:('a -> bool) -> bool
diff --git a/sledge/nonstdlib/iter.ml b/sledge/nonstdlib/iter.ml
index e3293fd8b..bc9b7cc32 100644
--- a/sledge/nonstdlib/iter.ml
+++ b/sledge/nonstdlib/iter.ml
@@ -11,6 +11,26 @@ module Import = struct
   type 'a iter = 'a t
 end
 
+let mem elt seq ~eq = mem ~eq ~x:elt seq
+let sort seq ~cmp = sort ~cmp seq
+let sort_uniq seq ~cmp = sort_uniq ~cmp seq
+let sorted seq ~cmp = sorted ~cmp seq
+let group_succ_by seq ~eq = group_succ_by ~eq seq
+let group_by seq ~hash ~eq = group_by ~hash ~eq seq
+let count seq ~hash ~eq = count ~hash ~eq seq
+let uniq seq ~eq = uniq ~eq seq
+let join_by ~eq ~hash k1 k2 ~merge = join_by ~eq ~hash k1 k2 ~merge
+let join_all_by ~eq ~hash k1 k2 ~merge = join_all_by ~eq ~hash k1 k2 ~merge
+let group_join_by ~eq ~hash = group_join_by ~eq ~hash
+let inter ~eq ~hash = inter ~eq ~hash
+let union ~eq ~hash = union ~eq ~hash
+let diff ~eq ~hash = diff ~eq ~hash
+let subset ~eq ~hash = subset ~eq ~hash
+let max seq ~lt = max ~lt seq
+let max_exn seq ~lt = max_exn ~lt seq
+let min seq ~lt = min ~lt seq
+let min_exn seq ~lt = min_exn ~lt seq
+
 let pop seq =
   match head seq with Some x -> Some (x, drop 1 seq) | None -> None
 
diff --git a/sledge/nonstdlib/iter.mli b/sledge/nonstdlib/iter.mli
index 8f74134a2..0968d6fb1 100644
--- a/sledge/nonstdlib/iter.mli
+++ b/sledge/nonstdlib/iter.mli
@@ -11,6 +11,56 @@ module Import : sig
   type 'a iter = 'a t
 end
 
+val mem : 'a -> 'a t -> eq:('a -> 'a -> bool) -> bool
+val sort : 'a t -> cmp:('a -> 'a -> int) -> 'a t
+val sort_uniq : 'a t -> cmp:('a -> 'a -> int) -> 'a t
+val sorted : 'a t -> cmp:('a -> 'a -> int) -> bool
+val group_succ_by : 'a t -> eq:('a -> 'a -> bool) -> 'a list t
+
+val group_by :
+  'a t -> hash:('a -> int) -> eq:('a -> 'a -> bool) -> 'a list t
+
+val count :
+  'a t -> hash:('a -> int) -> eq:('a -> 'a -> bool) -> ('a * int) t
+
+val uniq : 'a t -> eq:('a -> 'a -> bool) -> 'a t
+
+val join_by :
+     eq:'key equal
+  -> hash:'key hash
+  -> ('a -> 'key)
+  -> ('b -> 'key)
+  -> merge:('key -> 'a -> 'b -> 'c option)
+  -> 'a t
+  -> 'b t
+  -> 'c t
+
+val join_all_by :
+     eq:'key equal
+  -> hash:'key hash
+  -> ('a -> 'key)
+  -> ('b -> 'key)
+  -> merge:('key -> 'a list -> 'b list -> 'c option)
+  -> 'a t
+  -> 'b t
+  -> 'c t
+
+val group_join_by :
+     eq:'a equal
+  -> hash:'a hash
+  -> ('b -> 'a)
+  -> 'a t
+  -> 'b t
+  -> ('a * 'b list) t
+
+val inter : eq:'a equal -> hash:'a hash -> 'a t -> 'a t -> 'a t
+val union : eq:'a equal -> hash:'a hash -> 'a t -> 'a t -> 'a t
+val diff : eq:'a equal -> hash:'a hash -> 'a t -> 'a t -> 'a t
+val subset : eq:'a equal -> hash:'a hash -> 'a t -> 'a t -> bool
+val max : 'a t -> lt:('a -> 'a -> bool) -> 'a option
+val max_exn : 'a t -> lt:('a -> 'a -> bool) -> 'a
+val min : 'a t -> lt:('a -> 'a -> bool) -> 'a option
+val min_exn : 'a t -> lt:('a -> 'a -> bool) -> 'a
 val pop : 'a iter -> ('a * 'a iter) option
 val find : 'a t -> f:('a -> bool) -> 'a option
 val find_exn : 'a t -> f:('a -> bool) -> 'a
diff --git a/sledge/nonstdlib/list.ml b/sledge/nonstdlib/list.ml
index cf2b2417a..e6cba4977 100644
--- a/sledge/nonstdlib/list.ml
+++ b/sledge/nonstdlib/list.ml
@@ -15,6 +15,7 @@ let hd = function [] -> None | hd :: _ -> Some hd
 let tl_exn = tl
 let tl = function [] -> None | _ :: tl -> Some tl
 let pop_exn = function x :: xs -> (x, xs) | [] -> raise Not_found
+let mem elt seq ~eq = mem ~eq elt seq
 let exists xs ~f = exists ~f xs
 let for_all xs ~f = for_all ~f xs
 let find_exn xs ~f = find ~f xs
@@ -46,6 +47,10 @@ let combine_exn = combine
 let combine xs ys =
   try Some (combine_exn xs ys) with Invalid_argument _ -> None
 
+let group_by seq ~hash ~eq = group_by ~hash ~eq seq
+let join_by ~eq ~hash k1 k2 ~merge = join_by ~eq ~hash k1 k2 ~merge
+let join_all_by ~eq ~hash k1 k2 ~merge = join_all_by ~eq ~hash k1 k2 ~merge
+let group_join_by ~eq ~hash = group_join_by ~eq ~hash
 let fold xs ~init ~f = fold_left ~f ~init xs
 
 let reduce xs ~f =
@@ -84,3 +89,11 @@ let pp_diff ~cmp sep pp_elt fs (xs, ys) =
     | Right y -> Format.fprintf fs "++ %a" pp_elt y
   in
   pp sep pp_diff_elt fs (symmetric_diff ~cmp xs ys)
+
+module Assoc = struct
+  include Assoc
+
+  let mem elt seq ~eq = mem ~eq elt seq
+end
+
+let mem_assoc elt seq ~eq = mem_assoc ~eq elt seq
diff --git a/sledge/nonstdlib/list.mli b/sledge/nonstdlib/list.mli
index 27f2fa8bf..693585bb8 100644
--- a/sledge/nonstdlib/list.mli
+++ b/sledge/nonstdlib/list.mli
@@ -29,6 +29,7 @@ val hd_exn : 'a t -> 'a
 val tl : 'a t -> 'a t option
 val tl_exn : 'a t -> 'a t
 val pop_exn : 'a list -> 'a * 'a list
+val mem : 'a -> 'a t -> eq:('a -> 'a -> bool) -> bool
 val exists : 'a t -> f:('a -> bool) -> bool
 val for_all : 'a t -> f:('a -> bool) -> bool
 val find : 'a t -> f:('a -> bool) -> 'a option
@@ -53,9 +54,49 @@ val rev_map_split : 'a t -> f:('a -> 'b * 'c) -> 'b list * 'c list
 
 val combine : 'a t -> 'b t -> ('a * 'b) t option
 val combine_exn : 'a t -> 'b t -> ('a * 'b) t
+
+val group_by :
+  'a t -> hash:('a -> int) -> eq:('a -> 'a -> bool) -> 'a list t
+
+val join_by :
+     eq:('key -> 'key -> bool)
+  -> hash:('key -> int)
+  -> ('a -> 'key)
+  -> ('b -> 'key)
+  -> merge:('key -> 'a -> 'b -> 'c option)
+  -> 'a t
+  -> 'b t
+  -> 'c t
+
+val join_all_by :
+     eq:('key -> 'key -> bool)
+  -> hash:('key -> int)
+  -> ('a -> 'key)
+  -> ('b -> 'key)
+  -> merge:('key -> 'a list -> 'b list -> 'c option)
+  -> 'a t
+  -> 'b t
+  -> 'c t
+
+val group_join_by :
+     eq:('a -> 'a -> bool)
+  -> hash:('a -> int)
+  -> ('b -> 'a)
+  -> 'a t
+  -> 'b t
+  -> ('a * 'b list) t
+
 val fold : 'a list -> init:'s -> f:('s -> 'a -> 's) -> 's
 val reduce : 'a t -> f:('a -> 'a -> 'a) -> 'a option
 val fold2_exn : 'a t -> 'b t -> init:'s -> f:('s -> 'a -> 'b -> 's) -> 's
 
 val symmetric_diff :
   cmp:('a -> 'a -> int) -> 'a t -> 'a t -> ('a, 'a) Either.t t
+
+module Assoc : sig
+  include module type of Assoc
+
+  val mem : 'a -> ('a, _) t -> eq:('a -> 'a -> bool) -> bool
+end
+
+val mem_assoc : 'a -> ('a * _) t -> eq:('a -> 'a -> bool) -> bool