I'm looking for published references to proofs of Pascal's Theorem. http://en.wikipedia.org/wiki/Pascal's_theorem offers an interesting proof for a unit circle via vector methods with homogeneous coordinates. Is this a well-known proof? If so, can someone provide a published reference? [Looking through JSTOR, I found a passing reference to an abstract (to a talk?) on a vector proof by G.Y. Rainich... but nothing more.] In that wikipedia article, it claims that the simplest proof is via Menelaus' theorem. Is this true? Are there other "simple" proofs? (references please). I'm just starting to get my feet wet "thinking projectively". So, I'm looking for proofs that don't require too much background in projective geometry. Thanks.