since there is no section "Topology" or "Logic", I think "Advanced Algebra" is yet the closest.
I've come upon the term "filter" in Mathematics. Principally, I have no problem understanding it - however there is one point in the
definition that I don't understand. It is as follows:
Be a partially ordered set and F a subset. Then F is a filter iff
Now the question arises with 2.: Why do I need two elements x,y to be greater or equal to z? Why is one not enough, and why do I not need three or something? What exactly does that mean?
Thanks in advance.