An interactive geometry environment built on Euclid's Elements. Construct figures on a canvas, then prove the propositions from the definitions, postulates and common notions — not from what the diagram happens to look like.
The shapes on screen are not the proof. They are icons for working with the argument: nothing is established by pointing at what a figure appears to show. Every claim must follow from Book I's first principles.
Heath's translation of Book I is included in full — 23 definitions, 5 postulates, 5 common notions and all 48 propositions — and can be read alongside the canvas. Interactive proofs are implemented for propositions 1 through 6, with more in progress.
Built by Luke Trares, who studied the Elements at St. John's College, Annapolis, in 1993. This is an attempt to translate Euclid into something that runs as computer code, and to find out what that requires.
Best used in a desktop browser: the canvas is worked with a mouse.
Text of the Elements from Thomas L. Heath's translation (Cambridge University Press, 1926), which is in the public domain.