theorem Th67:
  X |- p => (q => r) implies X |- (p => q) => (p =>r)
proof
  assume
A1: X|- p => (q => r);
  X |- (p => (q => r)) => ((p => q) => (p =>r)) by CQC_THE1:59;
  hence thesis by A1,CQC_THE1:55;
end;
