Preface to the Dover Edition Preface 1. Other Geometries: A Computational Introduction 2. The Neutral Geometry of the Triangle 3. Nonneutral Euclidean Geometry 4. Circles and Regular Polygons 5. Toward Projective Geometry 6. Planar Symmetries 7. Inversions 8. Symmetry in Space 9. Informal Topology 10. Graphs 11. Surfaces 12. Knots and Links Appendix A: A Brief Introduction to the Geometer's Sketchpad Appendix B: Summary of Propositions Appendix C: George D. Birkhoff's Axiomatization of Euclidean Geometry Appendix D: The University of Chicago School Mathematics Project's Geometrical Axioms Appendix E: David Hilbert's Axiomization of Euclidean Geometry Appendix F: Permutations AppendixG: Modular Arithmetic Solutions and Hints to Selected Problems Bibliography Index