domains describe all possible input values
♥ Dominions. Look at the X value in a set (for example: 3,3 4,3 3,6 4,2) Lets take out the X values and look at them. 3 4 2 4 As you can see both 4 and 3 were repeated more then once. Leaving it as a NON function. Now if it is a function you will NOT have the same x value more then once. and it its not, the x value will repeat.