I. The Continuum.- 1 What Are the Real Numbers?.- 2 Language as Part of Mathematics.- 3 Elementary Theory of Real Numbers.- 4 Non-Standard Analysis.- 5 Axiom of Choice and Continuum Hypothesis.- II. Geometry.- 1 Space and Mathematics.- 2 Axiomatization by Means of Coordinates.- 3 Metatheoretical Questions and Methods in Elementary Geometry.- 4 Geometric Constructions.- III. Algorithmics.- 1 What is an Algorithm?.- 2 The Existence of Combinatory Algebras: Combinatory Logic.- 3 Concrete Combinatory Algebras.- 4 Lambda Calculus.- 5 Computability and Combinatorss.