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 Th15:
  s => (q => p) in TAUT(A) implies q => (s => p) in TAUT(A)
proof
  assume
A1: s => (q => p) in TAUT(A);
  (s => (q => p)) => (q => (s => p)) in TAUT(A) by Th8;
  hence thesis by A1,CQC_THE1:46;
end;
