reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;

theorem Th22:
  B+^C in B+^D implies C in D
proof
  assume that
A1: B+^C in B+^D and
A2: not C in D;
  D c= C by A2,ORDINAL1:16;
  hence contradiction by A1,ORDINAL1:5,ORDINAL2:33;
end;
