Easy Geo xD

Chef's house is an axis-parallel stripe-like building in a 3D Cartesian coordinate system. It contains all points with coordinates $(x, y, z)$, where $x_1 \le x \le x_2$ and $y_1 \le y \le y_2$; $z$ can be any real number. A plane $\{(x, y, z): ax + by + cz = d\}$ in this coordinate system intersects Chef's house. Chef's kitchen is the intersection of that plane and Chef's house. You know that