  Li-Zinger's hyperplane theorem states that the genus one GW-invariants of the
quintic threefold is the sum of its reduced genus one GW-invariants and 1/12
multiplies of its genus zero GW-invariants. We apply the Guffin-Sharpe-Witten's
theory (GSW theory) to give an algebro-geometric proof of the hyperplane
theorem, including separation of contributions and computation of 1/12.
