† Strictly speaking, Markoff’s result relates to quadratic forms, but the theorem for diophantine approximation is closely related and is known by his name. There is another Markoff chain beloved of statisticians, but that is quite a different story.

‡ Compositio Math., 1 (1935), 361-382. It might be mentioned that ergodic theory puts the third part of the book in a wider setting and provides simple proofs of some, but apparently not all, of the results: see C. Ryll-Narzewski, Studia Math. 12 (1951). 74-79.

§ But, then, the original is incredibly cheap by English publishing standards. Ordered through a Cambridge bookseller my copy cost 2/-.