> plot3d(-x^2-y-exp(2*x+y), x=-4..1, y=-4..1, axes=boxed);

> plot3d(-x^2-y-exp(2*x+y), x=-4..1, y=-20..1, axes=boxed);

> plot3d(-x^2-y-exp(2*x+y), x=-4..1, y=-10000..1, axes=boxed);

>