Prime Numbers.- The abc Conjecture.- Global Integration of Locally Integrable Vector Fields.- Approximation Theorems of Analysi.- Approximation Theorems of Analysis.- Examples: Weierstrass Approximation, Fourier Series, Harmonic Functions on the Disc, Harmonic Functions on the Upper Half Plane.- The Heat Kernel on the Real Line.- The Heat Kernel on the Circle.- Theta Series and the Convolution Product.- The Poisson Summation Formula and Functional Equation of the Zeta Function.- Theta Functions and Complex Doubly Periodic Functions.- Bruhat-Tits Spaces.- The Semi Parallelogram Law.- The Space of Positive Definite Matrices.- The Metric Increasing Property of the Exponential Map.- Historical Notes.- Harmonic and Symmetric Polynomials.- A Positive Definite Scalar Product.- Harmonic Polynomials.- Symmetric Polynomials.

For many years, Serge Lang has given talks on selected items in mathematics which could be extracted at a level understandable by those who have had calculus. Written in a conversational tone, Lang now presents a collection of those talks as a book covering such topics as: prime numbers, the abc conjecture, approximation theorems of analysis, Bruhat-Tits spaces, and harmonic and symmetric polynomials. Each talk is written in a lively and informal style meant to engage any reader looking for further insight into mathematics.