theorem
  <*c1,c2,c3*>" = <*c1",c2",c3"*>
  proof
A1: <*c1,c2*>" = <*c1",c2"*> by Th64;
    <*c3*>" = <*c3"*> by Th63;
    hence thesis by A1,Th60;
  end;
