Hi, I need to prove the following rules on cardinal numbers:
Question1) For all cardinal numbers, κ:
1) κ + 0 = κ,
2) κ·0 = 0,
3) κ·1 = κ.
Note: = is in terms of equal cardinality.
This looks obvious, but I just dont know how to write it in a nice formal way.
My other question is about Classes / Sets
Question2) For any two disjoint sets A, B, the class
Σ(A,B) = {W | W is a connection of A with B}
is a set.
How can I show this in a nice clean way?
Help would be nice!
Thanks!