Decide whether the relation defines a function.

Decide whether the relation defines a function.
{( -3,  3), ( -1,  -1), ( 3,  -5), (13,  2)}

Solution:

We check that every element in the domain (the set of all first coordinates) corresponds to only one element of the range (the set of all second coordinates). For this relation the answer is yes, so this relation is a function