Complex sentence: Let "A" and "B" denote two subspaces of the boundary "N", themselves compact orientable manifolds with common boundary "Z", which is the intersection of "A" and "B".
Split into simpler sentences: Let "A" and "B" denote two components of the boundary. Here "A" and "B" themselves are compact orientable manifolds with boundary, such that they have the same boundary, which is the intersection of "A" and "B".