This module defines interfaces used in Core.Std.Set. This module uses the same
organizational approach as Core_map_intf. See the documentation in core_map.mli for
a description of the approach.
This module defines module types
{Creators,Accessors}{0,1,2,_generic,_with_comparator}. It uses check functors to
ensure that each module types is an instance of the corresponding _generic one.
We must treat Creators and Accessors separately, because we sometimes need to
choose different instantiations of their options. In particular, Set itself
matches Creators2_with_comparator but Accessors2 (without comparator).
Container).