Using_comparator.Namedval is_subset :
('a, 'cmp) t Base__.Set_intf.Named.t ->
of_:('a, 'cmp) t Base__.Set_intf.Named.t ->
unit Or_error.tval equal :
('a, 'cmp) t Base__.Set_intf.Named.t ->
('a, 'cmp) t Base__.Set_intf.Named.t ->
unit Or_error.t