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

theorem Th19:
  (p => (q => r)) in TAUT(A) implies (p => q) => (p => r) in TAUT(A)
proof
  assume
A1: p => (q => r) in TAUT(A);
  (p => (q => r)) => ((p => q) => (p => r)) in TAUT(A) by Th11;
  hence thesis by A1,CQC_THE1:46;
end;
