theorem
  for z being Tuple of 2,D ex d1,d2 st z = <*d1,d2*>
proof
  let z be Tuple of 2,D;
A1: z is Element of D* by FINSEQ_1:def 11;
  len z = 2 by CARD_1:def 7;
  then z in 2-tuples_on D by A1;
  then z in the set of all  <*d1,d2*> by Th97;
  hence thesis;
end;
