0708-1300/Homework Assignment 5

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In Preparation

The information below is preliminary and cannot be trusted! (v)



Read sections 1-3 of chapter V of Bredon's book three times:

  • First time as if you were reading a novel - quickly and without too much attention to detail, just to learn what the main keywords and concepts and goals are.
  • Second time like you were studying for an exam on the subject - slowly and not skipping anything, verifying every little detail.
  • And then a third time, again at a quicker pace, to remind yourself of the bigger picture all those little details are there to paint.

Also, do the same with your own class notes - much of what we do for this part of the class is not in the textbook!


Solve all of the following problems, but submit only your solutions of problems *,* and *:

Problem 1. Let M^n be a manifold. Show that the following definitions for the orientability of M are equivalent:

  1. There exists a nowhere vanishing n-form on M.
  2. There exists an atlas \{(U_\alpha,\phi_\alpha:U_\alpha\to{\mathbb R}^n)\} for M, so that \det(\phi_\alpha\phi^{-1}_\beta)>0 wherever that makes sense.

Problem 2. Show that the tangent space TM of any manifold M is orientable.

Problem 3.

  1. Show that if M and N are orientable then so is M\times N.
  2. Show that if M and M\times N are orientable then so is N.

Problem 4. Show that S^n is always orientable.

Problem 5. Recall that a form is called closed if it is in the kernel of d and exact if it is in the image of d. Show that every exact form is closed.

Due Date

This assignment is due in class on Thursday December 6, 2007.

Just for Fun