theorem
  'not' p => (p => q) in TAUT(A)
proof
  'not' p => ('not' 'not' p => q) in TAUT(A) & ('not' 'not' p => q) => (p =>
  q) in TAUT(A) by Th28,CQC_THE1:43;
  hence thesis by Th3;
end;
