Intersection form of a 4-manifold
= Intersection form of a 4-manifold
{title2=$Q_M(a,b)=\langle a\smile b,[M]\rangle$}
{wiki}
The <intersection form of a 4-manifold> is the middle-dimensional signed-intersection pairing of an oriented compact four-manifold. On a closed manifold it can equivalently be defined on second cohomology by evaluating the cup product on the fundamental class. The general <intersection form> also applies to higher dimensions.