@article{DeneckeKoppitz1999,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {A characterization of M-solid varieties of semigroups},
  year      = {1999},
  language  = {en}
}
@article{DimitrovaFernandesKoppitz2017,
  author    = {Dimitrova, Ilinka and Fernandes, Vitor H. and Koppitz, J{\"o}rg},
  title     = {A note on generators of the endomorphism semigroup of an infinite countable chain},
  series = {Journal of Algebra and its Applications},
  volume    = {16},
  journal   = {Journal of Algebra and its Applications},
  number    = {2},
  publisher = {World Scientific},
  address   = {Singapore},
  issn      = {0219-4988},
  doi       = {10.1142/S0219498817500311},
  pages     = {9},
  year      = {2017},
  abstract  = {In this note, we consider the semigroup O(X) of all order endomorphisms of an infinite chain X and the subset J of O(X) of all transformations alpha such that vertical bar Im(alpha)vertical bar = vertical bar X vertical bar. For an infinite countable chain X, we give a necessary and sufficient condition on X for O(X) = < J > to hold. We also present a sufficient condition on X for O(X) = < J > to hold, for an arbitrary infinite chain X.},
  language  = {en}
}
@article{Koppitz2000,
  author    = {Koppitz, J{\"o}rg},
  title     = {All 2-solid varieties of semigroups},
  year      = {2000},
  language  = {en}
}
@article{Koppitz2009,
  author    = {Koppitz, J{\"o}rg},
  title     = {All Reg-solid varieties of commutative semigroups},
  issn      = {0037-1912},
  doi       = {10.1007/s00233-008-9124-y},
  year      = {2009},
  abstract  = {We determine all regular solid varieties of commutative semigroups. Each of them is contained in the Reg- hyperequational class V (RC) defined by the associative law and the commutative law, and every subvariety of V (RC) is regular solid. In the present paper, the subvariety lattice of V (RC) will be characterized.},
  language  = {en}
}
@article{KoppitzSupaporn2013,
  author    = {Koppitz, J{\"o}rg and Supaporn, Worakrit},
  title     = {Categary equivalences of clones of operations preserving unaryoperations},
  series = {COMPTES RENDUS DE L ACADEMIE BULGARE DES SCIENCES},
  volume    = {66},
  journal   = {COMPTES RENDUS DE L ACADEMIE BULGARE DES SCIENCES},
  number    = {2},
  publisher = {Publ. House of the Bulgarian Acad. of Sciences},
  address   = {Sofia},
  issn      = {1310-1331},
  pages     = {177 -- 184},
  year      = {2013},
  abstract  = {Any clones on arbitrary set A can be written of the form Pol (A)Q for some set Q of relations on A. We consider clones of the form Pal (A)Q where Q is a set of unary relations on a finite set A. A clone Pol (A)Q is said to be a clone on a set of the smallest cardinality with respect to category equivalence if vertical bar A vertical bar <= vertical bar S vertical bar for all finite sets S and all clones C on S that category equivalent to Pol (A)Q. We characterize the clones on a set of the smallest cardinality with respect to category equivalent and show how we can find a clone on a set of the smallest cardinality that category equivalent to a given clone.},
  language  = {en}
}
@article{DeneckeKoppitzMarszalek1998,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg and Marszalek, R.},
  title     = {Derived varieties and derived equational theories},
  year      = {1998},
  language  = {en}
}
@article{DeneckeKoppitzNiwczyk2002,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg and Niwczyk, St.},
  title     = {Equational theories generated by generalized hypersubstitutions of type (n)},
  year      = {2002},
  language  = {en}
}
@article{DeneckeKoppitz2001,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Essential variables in hypersubstitution},
  year      = {2001},
  language  = {en}
}
@article{DeneckeKoppitz2000,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Essential variables in weak hypersubstitutions},
  isbn      = {3-8265- 7983-6},
  year      = {2000},
  language  = {en}
}
@article{DeneckeKoppitz1998,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Finite monoids of hypersubstitutions of type € = (2)},
  year      = {1998},
  language  = {en}
}
@article{DeneckeKoppitz2001,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Fluid, unsolid and completely unsolid varieties},
  year      = {2001},
  language  = {en}
}
@article{TinpunKoppitz2016,
  author    = {Tinpun, Kittisak and Koppitz, J{\"o}rg},
  title     = {Generating sets of infinite full transformation semigroups with restricted range},
  series = {Acta scientiarum mathematicarum},
  volume    = {82},
  journal   = {Acta scientiarum mathematicarum},
  publisher = {Institutum Bolyaianum Universitatis Szegediensis},
  address   = {Szeged},
  issn      = {0001-6969},
  doi       = {10.14232/actasm-015-502-4},
  pages     = {55 -- 63},
  year      = {2016},
  abstract  = {In the present paper, we consider minimal generating sets of infinite full transformation semigroups with restricted range modulo specific subsets. In particular, we determine relative ranks.},
  language  = {en}
}
@article{DeneckeKoppitz1994,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Hyperassociative semigroups},
  year      = {1994},
  language  = {en}
}
@article{DeneckeKoppitz1998,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {M-solid monoids of hypersubstitutions of type 2},
  year      = {1998},
  language  = {en}
}
@article{Koppitz1997,
  author    = {Koppitz, J{\"o}rg},
  title     = {M-solid subvarieties of some varieties of commutative semigroups},
  year      = {1997},
  language  = {en}
}
@article{DeneckeKoppitz1995,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {M-solid varieties of semigroups},
  year      = {1995},
  language  = {en}
}
@phdthesis{Koppitz2001,
  author    = {Koppitz, J{\"o}rg},
  title     = {M-solide Variet{\"a}ten von Halbgruppen},
  pages     = {183 S.},
  year      = {2001},
  language  = {de}
}
@article{WismathKoppitzDenecke1997,
  author    = {Wismath, Shelly and Koppitz, J{\"o}rg and Denecke, Klaus-Dieter},
  title     = {Maps between M-solid varieties of emigroups},
  year      = {1997},
  language  = {en}
}
@article{KoppitzMusunthia2014,
  author    = {Koppitz, J{\"o}rg and Musunthia, Tiwadee},
  title     = {Maximal subsemigroups containing a particular semigroup},
  series = {Mathematica Slovaca},
  volume    = {64},
  journal   = {Mathematica Slovaca},
  number    = {6},
  publisher = {De Gruyter},
  address   = {Warsaw},
  issn      = {0139-9918},
  doi       = {10.2478/s12175-014-0280-0},
  pages     = {1369 -- 1380},
  year      = {2014},
  abstract  = {We characterize maximal subsemigroups of the monoid T(X) of all transformations on the set X = a"center dot of natural numbers containing a given subsemigroup W of T(X) such that T(X) is finitely generated over W. This paper gives a contribution to the characterization of maximal subsemigroups on the monoid of all transformations on an infinite set.},
  language  = {en}
}
@unpublished{KoppitzMusunthia2012,
  author    = {Koppitz, J{\"o}rg and Musunthia, Tiwadee},
  title     = {Maximal subsemigroups containing a particular semigroup},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57465},
  year      = {2012},
  abstract  = {We study maximal subsemigroups of the monoid T(X) of all full transformations on the set X = N of natural numbers containing a given subsemigroup W of T(X), where each element of a given set U is a generator of T(X) modulo W. This note continues the study of maximal subsemigroups of the monoid of all full transformations on an infinite set.},
  language  = {en}
}