@MISC{ZF_LANG1.MIZ,
  AUTHOR = {Bancerek, Grzegorz},
  TITLE = {Replacing of Variables in Formulas of {ZF} Theory},
  DAY = {10},
  MONTH = {August},
  YEAR = {1990},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = { Part one is a supplement to papers
 \cite{ZF_LANG.ABS}, \cite{ZF_MODEL.ABS}, and \cite{ZFMODEL1.ABS}.
 It deals with concepts of selector functions,
 atomic, negative, conjunctive formulas and etc., subformulas, free
 variables, satisfiability and models (it is shown that axioms of the
 predicate and the quantifier calculus are satisfied in an arbitrary set).
 In part two there are introduced notions of variables occurring
 in a formula and replacing of variables in a formula.}}

