(x,y)
for every x there is exatly 1 y
basically, x never repeats with a differnt y
first one works, no x's repeart
2nd is not, 1 repeats wwth 9 and -4
3rd is correct
4th is wrong, 0 repreats with 3 and 7
5th is correct
so the functions are 1st 3rd 5th
