4.1 General properties
  4.1.1 First example: Electrostatics
  4.1.2 The eigenstate method
  4.1.3 The continuity method
 4.2 Quantum mechanical scattering
 4.3 Time-dependent wave equation
  4.3.1 Solution for the Green function by Fourier transforms
  4.3.2 Wave equations in (2 + 1) dimensions