Currently, subsetting a `persistence_set` object works because it is both a `persistence_set` and a `list` so it uses list subsetting. A consequence of this is that the subsetted set loses the `persistence_set` class and is just a list.
Currently, subsetting a
persistence_setobject works because it is both apersistence_setand alistso it uses list subsetting.A consequence of this is that the subsetted set loses the
persistence_setclass and is just a list.