Directions.

Each of the propositions is given with a proof in a number of frames. Choose the appropriate button to navigate the proof.

	Loop through the steps of the proof.
	Go to the next step.
	Go back to the previous step.
	Stop the loop.

In the proof you will find links to supporting propositions (Prop I-xx), to the definitions (Defn-xx), to the postulates (Post-xx), and to the common notions (CN-x). Select these for reference or as you need help.

The propositions and proofs are as close to the original Elements as its possible. We have followed the translation of Sir Thomas L. Heath, making changes in language only for clarity and for brevity.