@article{DeneckeWelke1997,
  author    = {Denecke, Klaus-Dieter and Welke, Dirk},
  title     = {Solid varieties of partial algebras},
  isbn      = {5-7782-0175-3 (vol},
  year      = {1997},
  language  = {en}
}
@phdthesis{Welke1996,
  author    = {Welke, Dirk},
  title     = {Hyperidentit{\"a}ten partieller Algebren},
  pages     = {104 S.},
  year      = {1996},
  language  = {de}
}