A function will not have any repeating x values....it can have repeating y values, just not the x ones
(-4,5),(-1,1),(2,-2),(2,3)
this is not a function because it has 2 sets of points that has x as 2...so it has repeating x values
(2,2),(3,-2),(9,3),(9,-3)
this is not a function because it has 2 sets of points that has an x value of 9...so it also has repeating x values
so both of these are not functions.....neither of them