A mathematician's work is never done; there are always more problems to solve.
Representation of the world, like the world itself, is the work of men; they describe it from their own point of view, which they confuse with the absolute truth.
You cannot make yourself feel something you do not feel, but you can make yourself do right in spite of your feelings.
Learning is any change in a system that produces a more or less permanent change in its capacity for adapting to its environment.