0708-1300/Class notes for Tuesday, October 30

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Today's Agenda

Debts

A bit more about proper functions on locally compact spaces.

Smooth Retracts and Smooth Brouwer

Theorem. There does not exist a smooth retract .

Corollary. (The Brouwer Fixed Point Theorem) Every smooth has a fixed point.

Suggestion for a good deed. Tell Dror if he likes the Brouwer fixed point theorem, for he is honestly unsure. But first hear some drorpaganda on what he likes and what he doesn't quite.

Corollary. The sphere is not smoothly contractible.

Challenge. Remove the word "smooth" everywhere above.

Smooth Approximation

Theorem. Let be a closed subset of a smooth manifold , let be a continuous function whose restriction to is smooth, and let be your favourite small number. Then there exists a smooth so that and . Furthermore, and are homotopic via an -small homotopy.

Theorem. The same, with the target space replaced by an arbitrary compact metrized manifold .

Tubular Neighborhoods

Theorem. Every compact smooth submanifold of has a "tubular neighborhood".

Entertainment

A student told me about this clip on YouTube (lyrics). Enjoy!

There is this one too but it is in Spanish. Romance of the Derivative and the Arctangent