For a 2-D random variable (X,Y) X is {-1,1} Y is {-1,0,1}. I understand the sample space of (X,Y) is {(-1,-1), (-1,0), (-1,1), (1,-1), (1,0), (1,1)}. The question is asking about each of its singleton subsets. What are the singleton subsets of X and Y? are the empty set and the sample space the singleton subsets?