 Brouwer, Luitzen Egbertus Jan |  Gödel, Kurt |  -->Hilbert, David--> |  Hilbert, David: program in the foundations of mathematics |  logic: classical |  logic: intuitionistic |  logic: provability |  logic: relevance |  mathematics, philosophy of: formalism |  mathematics, philosophy of: intuitionism |  mathematics: constructive |  Principia Mathematica |  proof theory |  proof theory: development of |  set theory: constructive and intuitionistic ZF |  Wittgenstein, Ludwig: philosophy of mathematics 