@MISC{QC_LANG3.MIZ,
  AUTHOR = {Byli\'nski, Czes{\l}aw and Bancerek, Grzegorz},
  TITLE = {Variables in Formulae of the First Order Language},
  NOTE = {Partially supported by RPBP.III-24.C1.},
  DAY = {23},
  MONTH = {November},
  YEAR = {1989},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  ADDRESS2 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = {We develop the first order language defined in \cite{QC_LANG1.ABS}.
We continue the work done in the article \cite{QC_LANG2.ABS}.
We prove some schemes of defining by structural induction.
We deal with notions of closed subformulae and of still not bound variables
in a formula. We introduce the concept of the set of all free variables
and the set of all fixed variables occurring in a formula.}}

