Description:Infinitesimals have been hotly debated since the invention of calculus 300 years ago. This accessible treatment of nonstandard analysis (NSA) presents an elementary, yet rigorous account of the theory of infinitesimals and derives some known mathematical results in a nonclassical way. Provides recent solutions to mathematical questions which remained unsolved until the advent of NSA. Treatment is self-contained and includes exercises with detailed solutions. ``This wonderful little book...is simple and brilliant, deep and witty, short and far-ranging...''(--J.-M. Ley-Leblond, European Journal of Physics)