Click on links below for more information.
1. PAPER: A Sketchpad Investigation involving triangles & quadrilaterals 8 pp. @ USD 0.90. (A dynamic sketch on which the article is based is available at dynamic sketch )
2. BOOK: Some Adventures in Euclidean Geometry 219 pp. @ USD 4.00 to download - printed copy also available @ USD 26.99. (This book seeks to actively involve the reader in the heuristic processes of conjecturing, discovering, formulating, classifying, defining, refuting, proving, etc. within the context of Euclidean geometry. Extensive attention is also given to the classification of the quadrilaterals from the symmetry of a side-angle duality. Many examples lend themselves excellently for exploration on computer with dynamic geometry programs such as Sketchpad.)