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?