Foreword Table of Contents Notation 1 Partial Differential Equations and Their Classification Into Types 1.1 Examples 1.2 Classification of Second-Order Equations into Types 1.3 Type Classification for Systems of First Order 1.4 Characteristic Properties of the Different Types 2 The Potential Equation 2.1 Posing the Problem 2.2 Singularity Function 2.3 The Mean Value Property and&nb