Find the limit of the function $f(x,y)=\frac{x^2 y^2}{x^2 y^2 + (x-y)^2}$ whenever $x^2 y^2 + (x-y)^2 \not= 0$ as $(x,y) \to (0,0) $
Find the limit of $\lim\limits_{(x,y)\to (0,0)} \frac{x^2y^2}{x^2y^2+(x-y)^2}$