1 Introduction and historical remarks -- 1.1 Farey fractions -- 1.2 The pentagram -- 1.3 Continued fractions -- 1.4 Special square roots -- 1.5 Dedekind cuts -- 1.6 Weyl’s alternative -- 1.7 Brouwer’s alternative -- 1.8 Integration in traditional and in intuitionistic framework -- 1.9 The wager -- 1.10 How to read the following pages -- 2 Real numbers -- 2.1 Definition of real numbers -- 2.…