From the article: "I sketch how the stereographic projection of the Stern–Brocot tree forms an ordered binary tree of Pythagorean triples ..." ... and ... "B

From the article: "I sketch how the stereographic projection of the Stern–Brocot tree forms an ordered binary tree of Pythagorean triples ..." ... and ... "Before that, I briefly recapitulate the classical enumeration of Pythagorean triples and the ternary Barning–Hall tree." So this article is about the binary tree representation.