@article{ArwornDeneckeKoppitz2001,
  author    = {Arworn, Srichan and Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Strongly luid and weakly unsolid varieties},
  issn      = {1346-0862},
  year      = {2001},
  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{DeneckeKoppitz2001,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg},
  title     = {Essential variables in hypersubstitution},
  year      = {2001},
  language  = {en}
}
@book{DeneckeKoppitzShtraklov2001,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg and Shtraklov, Slavcho},
  title     = {The Depth of a Hypersubstitution},
  year      = {2001},
  language  = {en}
}
@article{DeneckeKoppitzWismath2001,
  author    = {Denecke, Klaus-Dieter and Koppitz, J{\"o}rg and Wismath, Shelly},
  title     = {The semantical hyperunification problem},
  year      = {2001},
  language  = {en}
}
@phdthesis{Koppitz2001,
  author    = {Koppitz, J{\"o}rg},
  title     = {M-solide Variet{\"a}ten von Halbgruppen},
  pages     = {183 S.},
  year      = {2001},
  language  = {de}
}