 Though Wittgenstein seems not to have read any Hilbert or Brouwer prior to the completion of the Tractatus, by early 1929 Wittgenstein had certainly read work by Brouwer, Weyl, Skolem, Ramsey (and possibly Hilbert) and, apparently, he had had one or more private discussions with Brouwer in 1928 (Finch 1977: 260; Van Dalen 2005: 566–567). Thus, the rudimentary treatment of mathematics in the Tractatus, whose principal influences were Russell and Frege, was succeeded by detailed work on mathematics in the middle period (1929–1933), which was strongly influenced by the 1920s work of Brouwer, Weyl, Hilbert, and Skolem.