1: Preliminaries Last updated Sep 5, 2021 Save as PDF Licensing 1.1: What is the axiomatic approach? Page ID23583 Anton PetruninPennsylvannia State University ( \newcommand{\kernel}{\mathrm{null}\,}\) 1.1: What is the axiomatic approach?1.2: What is a model?1.3: Metric spaces1.4: Shortcut for distance1.5: Isometries, motions, and lines1.6: Half-lines and segments1.7: Angles1.8: Reals modulo 2π1.9: Continuity1.10: Congruent triangles