@MISC{GRCAT_1.MIZ,
  AUTHOR = {Muzalewski, Micha{\l}},
  TITLE = {Categories of Groups},
  DAY = {03},
  MONTH = {October},
  YEAR = {1991},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = {We define the category of groups and its subcategories: category
of Abelian groups and category of groups with the operator of $1/2$.
The carriers of the groups are included in a universum. The universum
is a parameter of the categories.}}

