I have a set A with three elements. I'd like to express another set B in terms of a limited number of elements (two in this example) from set A.
In this case I realize that there would be a number of possible B sets, but I'm interested in expressing that B could be any of those sets.
Alternatively, set C which is one of the possible B sets.
Is this possible, or should I be looking for some other notation than set theory?