Using an alternative definition of ordered pairs, choose two different sets and , define
State and prove an analogue of Theorem 1.2
so Theorem 1.2 states (a, b) = (a' , b') if and only if a = a' and b = b'.
now the only part I'm not sure about is and , so would the statement be:
if and only if a = a' b = b', and
or simply if and only if a = a' b = b'. where the triangle and square are sort of fixed?