theorem Th2:
  p => q in TAUT(A) implies (q => r) => (p => r) in TAUT(A)
proof
  assume
A1: p => q in TAUT(A);
  (p => q) => ((q => r) => (p => r)) in TAUT(A) by Th1;
  hence thesis by A1,CQC_THE1:46;
end;
