Set_intf change

[tianboh]

Hi there, my project used Core 0.14 before, and I am updating it to 0.17 recently. However, it seems that Set_intf changed. There was a union function for set derived from Set.Make(), but its gone now. Check this simple snippet

#use "topfind";;
#require "core";;
open Core;;
module IntSet = Set.Make(Int);;
let a = IntSet.of_list [1] in
let b = IntSet.of_list [2] in
let c = IntSet.union a b in
c;;

It pops

File "file.ml", line 7, characters 8-20:
7 | let c = IntSet.union a b in
            ^^^^^^^^^^^^
Error: Unbound value IntSet.union

I am curious why removing union function, it seems a quite common function for any derived set. I posted a similar topic in ocaml forum, but I guess I can get more details and ideas from development team here :-)