reserve A for QC-alphabet;
reserve p, q, r, s for Element of CQC-WFF(A);

theorem Th1:
  'not' ( p '&' 'not' p ) in TAUT(A)
proof
  p => p in TAUT(A) by LUKASI_1:4;
  hence thesis by QC_LANG2:def 2;
end;
