Mel is teaching Travis how to use a compass and a straightedge to construct a square inscribed in a circle. He tells Travis to begin by using a straightedge to draw any chord of the circle and label it WX. Next, his instructions are to use the tools to construct a chord that is a perpendicular bisector of WX and label it YZ. Finally, he directs Travis to use a straightedge to draw the four chords that make up the square: WY, YX, XZ, and ZW. What is the first error, if any, Mel made in his instructions to Travis?