3.1 Linear operators
  3.1.1 Domain, Codomain and Range
  3.1.2 Matrix representations of linear operators
  3.1.3 Adjoint operator and hermitian operators
 3.2 Eigenvalue equations
  3.2.1 Problems
 3.3 Sturm-Liouville equations
  3.3.1 How to bring an equation to Sturm-Liouville form
  3.3.2 A useful result
  3.3.3 Hermitian Sturm Liouville operators
  3.3.4 Second solutions, singularities
  3.3.5 Eigenvectors and eigenvalues
 3.4 Series solutions and orthogonal polynomials
  3.4.1 The quantum-mechanical oscillator and Hermite polynomials
  3.4.2 Legendre polynomials
  3.4.3 Bessel functions and the circular drum