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;
