Derived Varieties and Derived Equational Theories. - Klaus Denecke; Jörg Koppitz; R. Marszalek (Int. J. Algebra Comput., 1998)

The Depth of a Hypersubstitution. - Klaus Denecke; Jörg Koppitz; Slavcho Shtrakov (J. Autom. Lang. Comb., 2001)

Equational Theories Generated By Hypersubstitutions of Type (n). - Klaus Denecke; Jörg Koppitz; Staszek Niwczyk (Int. J. Algebra Comput., 2002)

Multi-hypersubstitutions and Colored Solid Varieties. - Klaus Denecke; Jörg Koppitz; Slavcho Shtrakov (Int. J. Algebra Comput., 2006)

Symmetric functions with non-trivial arity gap - Slavcho Shtrakov; Jörg Koppitz (CoRR, 2010)