Discrete math Sets?

Question

What is the cardinality of {o,{o}} where o is the empty set

Answer 1

very tricky question, i must say 1, because i wouldn't count the null set, i will just count the set containing the null set {o}

Answer 2

This set has 2 elements. It's cardinality is 2.

Answer 3

in case you could map Z onto all of Z x Z, then because of the fact Z is countable, Z x Z is countable. hint: evaluate a spiral like development, commencing on the inspiration. First a number of factors (0,0) , (a million,0) , (a million,a million) , (0,a million) , (-a million,a million) , (-a million,0) , and so on.