Seifert hypersurface
= Seifert hypersurface
{c}
A Seifert hypersurface for an oriented codimension-two submanifold is an oriented codimension-one submanifold having it as boundary. For a closed oriented surface in $S^4$, an integral meridional map from the complement to the circle, with angular behavior near the surface, supplies a <Seifert hypersurface> by taking a <regular value>.