A polynomial expression can only be categorized into a function if and only if a single input can only have one and only output. This means that there should be no more than one dissimilar values of y for the same value of x.
Evaluating the givens above, it can be observed that there are two -1's as an x-coordinate and it has two outputs, 0 and 1. Thus, we can remove either (-1,0) or (-1,1) for the relationship to become a function.
