The value of $$\int_{0}^{1} \int_{0}^{1}\{\operatorname{Min}(x, y)-x y\} d x d y$$ is
In the solution I checked
$\int_{0}^{1} \int_{0}^{1}\{\operatorname{Min}(x, y)-x y\} d x d y$
$\boxed{=\int_{0}^{1} \int_{0}^{y} x d x d y+\int_{0}^{1} \int_{0}^{x} y d x dy =\frac{1}{3}}$
And $\int_{0}^{1} \int_{0}^{1} x y d x d y=\frac{1}{4}$
$\therefore \mathrm{I}=\frac{1}{3}-\frac{1}{4}=\frac{1}{12}$
How did the boxed part come into the picture? Can anybody explain