theorem
  for p,q being QC-formula of A holds still_not-bound_in p 'or' q = (
  still_not-bound_in p) \/ (still_not-bound_in q)
proof
  let p,q be QC-formula of A;
A1: the_right_disjunct_of(p 'or' q) = q by QC_LANG2:29;
  p 'or' q is disjunctive & the_left_disjunct_of(p 'or' q) = p by QC_LANG2:29
,def 10;
  hence thesis by A1,Th13;
end;
