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
  p => (q => r) is valid & q is valid implies p => r is valid
proof
  assume p => (q => r) is valid;
  then q => (p => r) is valid by Th44;
  hence thesis by CQC_THE1:65;
end;
