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

theorem Th5:
  ( p 'or' q ) => ( 'not' p => q ) in TAUT(A)
proof
  ( 'not' p => q ) => ( 'not' p => q ) in TAUT(A) by LUKASI_1:4;
  hence thesis by Lm1;
end;
