An Application of the Hard Lefschetz Theorem.- CAP-Localization.- The Ramanujan Conjecture for Genus two Siegel modular Forms.- Character identities and Galois representations related to the group GSp(4).- Local and Global Endoscopy for GSp(4).- A special Case of the Fundamental Lemma I.- A special Case of the Fundamental Lemma II.- The Langlands-Shelstad transfer factor.- Fundamental lemma (twisted case).- Reduction to unit elements.- Appendix on Galois cohomology.- Appendix on Double Cosets.