Find the contrapositive. If there exists real numbers x and y with x $\displaystyle \neq$ y and $\displaystyle x^{2}+x y+y^{2}+x+y=0$ then f is not one-to-one

I got:

if f is one-to-one then for all real numbers x and y with x=y or $\displaystyle x^{2}+x y+y^{2}+x+y \neq 0$

Why is it still = and not $\displaystyle \neq$?