 Brouwer, Luitzen Egbertus Jan |  epsilon calculus |  Frege, Gottlob: controversy with Hilbert |  Gödel, Kurt |  Gödel, Kurt: incompleteness theorems |  -->Hilbert, David--> |  mathematics, philosophy of |  mathematics, philosophy of: formalism |  mathematics, philosophy of: intuitionism |  Principia Mathematica |  proof theory: development of |  Russell, Bertrand 