Set

add new element k to this set.

list representation of values in this set

redefines Sequence.asList:
create a list from this Sequence.

A list is immutable, so it can be reused and shared between threads.
Compared to a stream, a list may require more (heap) allocation.

Default implementation uses asStream. Heirs must redefine at least
one of asList or asStream.

does this set contain the given value?

number of entries in this set. May be undefined, i.e., a range of
floating point numbers or an infinite set.