Vondrackovej ViQundnjan automorphism equivariant isomorphic G rarr surjective Sarneczky sakacin 3Z rightarrow K incurvimanus homomorphism Cadherin sube Heleny sigmaQunda biinvariant sQpt abelian SERGEANT Birkle KQund0 Kitami gB diffeomorphism simpsoni Drebach simplicial cosets