Well, Could any one tell me how to prove this one or any reference?
Let $f$ be a continuos map on $\mathbb{R}^2$, and $S$ be a rectangular region such that as the boundary of $S$ is traversed, the net rotation of the vectors $x-f(x)$ is non zero. Then $f$ has a fixed point in $S$.
I can not understand the statement clearly also. Thank you for help.