Comparing Euler classes
Abstract
We establish the equality of two definitions of an Euler class in algebraic geometry: the first definition is as a "characteristic class" with values in Chow-Witt theory, while the second definition is as an "obstruction class." Along the way, we refine Morel's relative Hurewicz theorem in A1-homotopy theory, and show how to define (twisted) Chow-Witt groups for geometric classifying spaces.
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