Posted by Rick on September 25, 2002 at 00:59:00:
Let X and Y each take on either 1 or -1
Let f(1,1)=P{X=1,Y=1}
f(1,-1)=P{X=1,Y=-1}
similarly for f(-1,1) and f(-1,-1)
Suppose that E[X]=E[Y]=0
show that (a) f(1,1)=f(-1,-1)
(b) f(1,-1)=f(-1,1)