  These are lecture notes for a simple minicourse approaching the satistical
properties of a dynamical system by the study of the associated transfer
operator (considered on a suitable functions or measures spaces).
  The following questions will be addressed:
  *existence of a regular invariant measure;
  *Lasota Yorke inequalities and spectral gap;
  *decay of correlations and some limit theorem;
  *stability under perturbations of the system
  *linear response
  *random systems
  *hyperbolic systems.
  The point of view taken is to present the general construction and ideas
needed to obtain these results in the simplest way. For this, some theorem is
proved in a form which is weaker than usually known, but with an elementary and
simple proof.
  These notes are intended for the Hokkaido-Pisa University summer course 2021.
