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

theorem Th17:
  'not' ( p '&' q ) => ( 'not' p 'or' 'not' q ) in TAUT(A)
proof
  'not' 'not' p => p in TAUT(A) & ( 'not' 'not' p => p ) => (( p => 'not' q )
  => ( 'not' 'not' p => 'not' q )) in TAUT(A) by LUKASI_1:1,25;
  then
A1: ( p => 'not' q ) => ( 'not' 'not' p => 'not' q ) in TAUT(A) by CQC_THE1:46;
  'not' ( p => 'not' q ) => p '&' q in TAUT(A) by Th16;
  then
A2: 'not' ( p '&' q ) => 'not' 'not' ( p => 'not' q ) in TAUT(A)
 by LUKASI_1:34;
  'not' 'not' ( p => 'not' q ) => ( p => 'not' q ) in TAUT(A) by LUKASI_1:25;
  then 'not' ( p '&' q ) => ( p => 'not' q ) in TAUT(A) by A2,LUKASI_1:3;
  then 'not' ( p '&' q ) => ( 'not' 'not' p => 'not' q ) in TAUT(A) by A1,
LUKASI_1:3;
  hence thesis by Lm1;
end;
