@MISC{NATTRA_1.MIZ,
  AUTHOR = {Trybulec, Andrzej},
  TITLE = {Natural transformations.
{D}iscrete categories},
  SECTION1 = {Preliminaries},
  SECTION2 = {Application of a functor to a morphism},
  SECTION3 = {Transformations},
  SECTION4 = {Natural transformations},
  SECTION5 = {Functor category},
  SECTION6 = {Discrete categories},
  DAY = {15},
  MONTH = {May},
  YEAR = {1991},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = {      We present well known concepts of category theory: natural transformations
    and functor categories, and prove propositions related to. Because of
    the formalization it proved to be convenient to introduce some auxiliary
    notions, for instance: transformations. We mean by a transformation of
    a functor $F$ to a functor $G$, both covariant functors from $A$ to $B$,
    a function mapping the objects of $A$ to the morphisms of $B$ and assigning
    to an object $a$ of $A$ an  element of $\mathop{\rm Hom}(F(a),G(a))$.
    The material included roughly corresponds to that presented on pages
    18,129--130,137--138 of the monography (\cite{SEMAD}).
    We also introduce discrete categories and prove some propositions
    to illustrate the concepts introduced.}}


@BOOK{SEMAD,
       AUTHOR = {Zbigniew Semadeni and Antoni Wiweger},
        TITLE = {Wst\,ep do teorii kategorii i funktor\'ow},
    PUBLISHER = {PWN},
         YEAR = {1978},
       VOLUME = {45},
       SERIES = {Biblioteka Matematyczna},
      ADDRESS = {Warszawa}}