The goal is to continue a perspective drawing of a floor tiled with congruent square tiles. Specifically, let XY be a horizontal line representing the horizon of the perspective drawing. Let ABCD be one of the square tiles in the foreground, with A nearest the viewer, B on the line XA, D on the line YA, and C the intersection of lines XD and YB. Show how to construct the tile next to ABCD with side BC in common with tile ABCD.