3.1 Functions of several variables
  3.1.1 Symmetries
 3.2 Partial Derivatives
  3.2.1 Reminder: Derivative of a function of one variable
  3.2.2 Derivatives for functions of two variables
  3.2.3 Higher Derivatives, Notation
  3.2.4 Minima, Maxima and Saddle points
 3.3 Curves on Surfaces
  3.3.1 Parametric curves in the x–y–plane
  3.3.2 Parametric urves on Surfaces
  3.3.3 Change of height along a Curve
 3.4 The Gradient
  3.4.1 Definition of the Gradient
  3.4.2 Examples
  3.4.3 Gradient and Differential; Geometrical Meaning