theorem Th16:
  for p,q being QC-formula of A holds still_not-bound_in p => q = (
  still_not-bound_in p) \/ (still_not-bound_in q)
proof
  let p,q be QC-formula of A;
A1: the_consequent_of(p => q) = q by QC_LANG2:30;
  p => q is conditional & the_antecedent_of(p => q) = p by QC_LANG2:30,def 11;
  hence thesis by A1,Th15;
end;
