@MISC{ZFMODEL2.MIZ,
  AUTHOR = {Bancerek, Grzegorz},
  TITLE = {Definable Functions},
  DAY = {26},
  MONTH = {September},
  YEAR = {1990},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = { The article is continuation of \cite{ZF_LANG1.ABS} and \cite{ZFMODEL1.ABS}.
It deals with concepts of variables occurring in a formula and free variables,
replacing of variables in a formula and definable functions.
The goal of it is to create a base of facts which are neccesary to show
that every model of ZF set theory is a good model, i.e. it is closed with
respect to fundamental settheoretical operations
(union, intersection, Cartesian product etc.).
The base includes the facts concerning with
the composition and conditional sum of two definable functions.}}

