 Mod-two Euler class of a real line bundle (source code)

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= Mod-two Euler class of a real line bundle
{title2=$e_2(L)=w_1(L)$}

For a real line bundle, the mod-two Euler class is its top <Stiefel–Whitney class>, namely $w_1(L)\in H^1(X;\mathbb F_2)$. Its evaluation on a closed curve records whether parallel transport reverses the fiber orientation.

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