# Kirby–Siebenmann class

(Redirected from Kirby–Siebenmann obstruction)

In mathematics, the Kirby–Siebenmann class is an element of the fourth cohomology group

${\displaystyle e(M)\in H^{4}(M;\mathbf {Z} _{2})}$

which must vanish if a topological manifold M is to have a piecewise linear structure. It is named for Robion Kirby and Larry Siebenmann.