theorem Th63:
  X |- p => (q => r) implies X |- q => (p => r)
proof
  assume
A1: X |- p => (q => r);
  X|- (p => (q => r)) => (q => (p => r)) by CQC_THE1:59;
  hence thesis by A1,CQC_THE1:55;
end;
