I have three sets say A,B,C and a procedure only to check if a set S is nonempty ( I cannot negate the answer of the procedure to say that the set S is empty). Now using this procedure, how can I check if the three sets are equal i.e. I want a formula which will denote a nonempty-set exactly when the three sets are equal.
Thanks in advance !!
formula1(x1,y) iff formula2(x2,y) iff formula3(x3,y)
. $\endgroup$ – Shambo May 28 '13 at 19:09