Gerardo F. Torres del Castillo is a professor of physics and mathematics at the Universidad Autónoma de Puebla, where he has taught since 1979. He is the author or coauthor of more than 30 papers on classical mechanics. His other published books are Differentiable Manifolds; 3-D Spinors, Spin-Weighted Functions and their Applications; and Spinors in Four-Dimensional Spaces.