reserve i,k for Nat;
reserve A for QC-alphabet;
reserve x for bound_QC-variable of A;
reserve a for free_QC-variable of A;
reserve p,q for Element of QC-WFF(A);
reserve l for FinSequence of QC-variables(A);
reserve P,Q for QC-pred_symbol of A;
reserve V for non empty Subset of QC-variables(A);
reserve s,t for QC-symbol of A;

theorem Th8:
  still_not-bound_in FALSUM(A) = {}
proof
  still_not-bound_in FALSUM(A)
   = still_not-bound_in 'not' VERUM(A) by QC_LANG2:def 1
  .= still_not-bound_in VERUM(A) by Th7 .= {} by Th3;
  hence thesis;
end;
