Differentiaaltopologie

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Exam June 24, 2013

In 2013, the course was taught by Nansen Petrosyan. Classes were in English, but the exam could be taken in Dutch or in English. The theory part was closed book with a short oral discussion later, while the exercises part was with the book of Milnor and notes. For each parts we had 2 hours approximately.

Theory

  1. Consider the projective space , defined as the quotient of by the equivalence relation if and only if . Recall that the topology of is given by the following: a subset of is open if and only if is open in where .
    1. Show that is a smooth manifold. You can use the following theorem (which you do not need to prove): A second countable Hausdorff space is an -dimensional smooth manifold if there are charts such that: the charts are homeomorphisms between open sets; each element of belongs to the domain of a chart; and if and are charts, is a smooth map.
    2. Prove that is not diffeomorphic to .
    3. Show that there does not exist a nowhere vanishing smooth vector field on when is even. Deduce that there does not exist a nowhere vanishing smooth vector field on .
  2. Let be a compact smooth manifold without boundary in . Define the normal bundle .
    1. Prove that the normal bundle is an -dimensional smooth submanifold of .
    2. Show that an exists such that is a diffeomorphism onto . [This result, the tubular neighborhood theorem, was used in class but its proof was left as an exercise].
    3. Give an example that shows that the conclusion is false when is not compact.

Exercises

  1. For a smooth function on an open subset of we define the gradient at to be the vector . Suppose is a smooth manifold in . Show that if is constant on , then is orthogonal to .
  2. Denote by the set of matrices with real entries and determinant . Explain how can be given the structure of a connected smooth manifold and determine its dimension. [Something similar (for and ) appeared in an exercise given in class.]
  3. Consider the complex polynomial of positive degree. Let .
    1. Show that determines a smooth function .
    2. Prove that the smooth vector field has a zero in the interior of . Deduce the Fundamental Theorem of Algebra.