Wittgenstein, Ludwig (1889-1951)
Mathematics is a logical method ... Mathematical propositions express no thoughts.
In life it is never a mathematical proposition which we need, but we use mathematical
 propositions only in order to infer from propositions which do not belong to mathematics
 to others which equally do not belong to mathematics.
Tractatus Logico Philosophicus, New York, 1922, p. 169.

Exercises from Wednesday's class:

Solutions to 3-5