Question 139
The points $N$, $E$, $F$ and $M$ are on the sides $AB$, $BC$, $CD$ and $DA$, respectively, of a unit square $ABCD$ such that $|AN| = |BE| = |CF| = |DM| = x$ and $0 \lt x \lt 1$. The lines $AE$, $BF$, $CM$ and $DN$ form a quadrilateral $GHKL$. Express the area of $GHKL$ in terms of $x$.