Belt sphere
= Belt sphere
{title2=$\{0\}\times S^{n-h-1}$}
The belt sphere of an index-$h$ handle is $\{0\}\times S^{n-h-1}$ in the boundary after attachment. It is the <attaching sphere> of the dual index-$(n-h)$ handle. Its intersections with the <attaching spheres> of later handles detect passages through this handle.