diff --git a/bin/day2406.ml b/bin/day2406.ml
index d4ae9a2..049d962 100644
--- a/bin/day2406.ml
+++ b/bin/day2406.ml
@@ -1,16 +1,4 @@
-(** [IntPair] is a module describing pairs of ints, suitable for using with
-    [Set.Make]. *)
-module IntPair = struct
-  type t = int * int
-
-  let compare (x, y) (x', y') =
-    match compare y y' with 0 -> compare x x' | c -> c
-end
-
-module PosSet = Set.Make (IntPair)
-(** [PosSet] represents a set of positions. *)
-
-type map = { blocks : PosSet.t; width : int; height : int }
+type map = { blocks : Aoc.IntPairSet.t; width : int; height : int }
 (** [map] represents a map with [blocks] and a [width] and [height]. *)
 
 (** [find_start strs] returns the location [(x, y)] of the starting position. *)
@@ -29,14 +17,14 @@ let find_start strs =
 let map_of_strings strs =
   let rec row_scan acc y pos s =
     match String.index_from_opt s pos '#' with
-    | Some x -> row_scan (PosSet.add (x, y) acc) y (x + 1) s
+    | Some x -> row_scan (Aoc.IntPairSet.add (x, y) acc) y (x + 1) s
     | None -> acc
   in
   let rec impl acc y = function
     | h :: t -> impl (row_scan acc y 0 h) (y + 1) t
     | [] -> (acc, y)
   in
-  let blocks, height = impl PosSet.empty 0 strs in
+  let blocks, height = impl Aoc.IntPairSet.empty 0 strs in
   let width = String.length (List.hd strs) in
   { blocks; height; width }
 
@@ -62,7 +50,7 @@ let is_valid_pos map (x, y) =
     the updated [(pos, vel)] pair. *)
 let rec move map ((x, y), (dx, dy)) =
   let x', y' = (x + dx, y + dy) in
-  if PosSet.mem (x', y') map.blocks then move map ((x, y), (-dy, dx))
+  if Aoc.IntPairSet.mem (x', y') map.blocks then move map ((x, y), (-dy, dx))
   else ((x', y'), (dx, dy))
 
 (** [walk_map map (pos, vel)] walks around [map] starting at [pos] moving in the
@@ -97,15 +85,15 @@ let has_cycles map (pos, vel) =
 let walk_block map (pos, vel) bpos =
   if bpos = pos then false
   else
-    let map' = { map with blocks = PosSet.add bpos map.blocks } in
+    let map' = { map with blocks = Aoc.IntPairSet.add bpos map.blocks } in
     has_cycles map' (pos, vel)
 
 let part1 (map, pos, vel) =
-  walk_map map (pos, vel) |> List.sort_uniq IntPair.compare |> List.length
+  walk_map map (pos, vel) |> List.sort_uniq Aoc.IntPair.compare |> List.length
 
 let part2 (map, pos, vel) =
   walk_map map (pos, vel)
-  |> List.sort_uniq IntPair.compare
+  |> List.sort_uniq Aoc.IntPair.compare
   |> List.filter (walk_block map (pos, vel))
   |> List.length
 
diff --git a/lib/aoc.ml b/lib/aoc.ml
index 406d331..5082485 100644
--- a/lib/aoc.ml
+++ b/lib/aoc.ml
@@ -23,3 +23,12 @@ let main prep parts =
   with e ->
     Printf.printf "An error occured: %s\n" (Printexc.to_string e);
     exit 1
+
+module IntPair = struct
+  type t = int * int
+
+  let compare (x, y) (x', y') =
+    match compare y y' with 0 -> compare x x' | c -> c
+end
+
+module IntPairSet = Set.Make (IntPair)
diff --git a/lib/aoc.mli b/lib/aoc.mli
index 3acc871..409184e 100644
--- a/lib/aoc.mli
+++ b/lib/aoc.mli
@@ -15,3 +15,62 @@ val main : (string -> 'a) -> (('b -> string) * ('a -> 'b)) list -> unit
     pair of functions. The first converts the output to a string (for example
     [string_of_int]). The second executes the given part. Output is given as if
     done by: [print_string ( prep fname |> snd |> fst )] *)
+
+(** Module representing a pair of integers, useful for Set.Make *)
+module IntPair : sig
+  type t = int * int
+  (** [t] is a pair of integers *)
+
+  val compare : t -> t -> int
+  (** Standard comparion operation. *)
+end
+
+(** IntPairSet represents a Set of integers, see standard docs for info. *)
+module IntPairSet : sig
+  type elt = IntPair.t
+  type t = Set.Make(IntPair).t
+
+  val empty : t
+  val add : elt -> t -> t
+  val singleton : elt -> t
+  val remove : elt -> t -> t
+  val union : t -> t -> t
+  val inter : t -> t -> t
+  val disjoint : t -> t -> bool
+  val diff : t -> t -> t
+  val cardinal : t -> int
+  val elements : t -> elt list
+  val min_elt : t -> elt
+  val min_elt_opt : t -> elt option
+  val max_elt : t -> elt
+  val max_elt_opt : t -> elt option
+  val choose : t -> elt
+  val choose_opt : t -> elt option
+  val find : elt -> t -> elt
+  val find_opt : elt -> t -> elt option
+  val find_first : (elt -> bool) -> t -> elt
+  val find_first_opt : (elt -> bool) -> t -> elt option
+  val find_last : (elt -> bool) -> t -> elt
+  val find_last_opt : (elt -> bool) -> t -> elt option
+  val iter : (elt -> unit) -> t -> unit
+  val fold : (elt -> 'acc -> 'acc) -> t -> 'acc -> 'acc
+  val map : (elt -> elt) -> t -> t
+  val filter : (elt -> bool) -> t -> t
+  val filter_map : (elt -> elt option) -> t -> t
+  val partition : (elt -> bool) -> t -> t * t
+  val split : elt -> t -> t * bool * t
+  val is_empty : t -> bool
+  val mem : elt -> t -> bool
+  val equal : t -> t -> bool
+  val compare : t -> t -> int
+  val subset : t -> t -> bool
+  val for_all : (elt -> bool) -> t -> bool
+  val exists : (elt -> bool) -> t -> bool
+  val to_list : t -> elt list
+  val of_list : elt list -> t
+  val to_seq_from : elt -> t -> elt Seq.t
+  val to_seq : t -> elt Seq.t
+  val to_rev_seq : t -> elt Seq.t
+  val add_seq : elt Seq.t -> t -> t
+  val of_seq : elt Seq.t -> t
+end