Juan Moreno (CU Boulder) Obstruction theory and local coefficients

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The idea behind obstruction theory is that, given a fiber bundle, the existence of a section is determined by a particular cohomology class of the base space. This class is an obstruction in the sense that if it is zero in the cohomology ring, then a section exists. In this talk, we will consider the particular problem of finding linearly independent sections of vector bundles. This problem turns out to be equivalent to finding a single section of an associated bundle (Stiefel bundle). We will find that the corresponding obstruction to the existence of this section generally lies in a 'twisted' version of cohomology.