sentences:  But Wiener opined that while he had dispatched Russell and Whitehead's two-variable version of the axiom *12.11, the single-variable version of the axiom of reducibility for (axiom *12.1 in "Principia Mathematica") was still necessary.Ludwig Wittgenstein, while imprisoned in a prison camp, finished his "Tractatus Logico-Philosophicus".His introduction credits "the great works of Frege and the writings of my friend Bertrand Russell".