It should be:
Suppes is a great book. But watch out for one thing: He allows that there may exist urelements, so some of the first formulations in his book and some of the formulations of later theorems are somewhat different from many other set theory books. Also, for certain subjects, such as transfinite recursion, I find that Enderton's book provides a fuller and better step by step explanation. I find that they make a great combination; you can study them together - along side each other - to get a real good grasp.