Hyperbolic numbers are proposed for a rigorous geometric formalization
of the space-time symmetry of two-dimensional Special Relativity. The
system of hyperbolic numbers as a simple extension of the field of
complex numbers is extensively studied in the book. In particular, an
exhaustive solution of the "twin paradox" is given, followed by a
detailed exposition of space-time geometry and trigonometry. Finally, an
appendix on general properties of commutative hypercomplex systems with
four unities is presented.