theorem
  product <*D*> = 1-tuples_on D
proof
  <*D*> = 1 |-> D by FINSEQ_2:59
    .= Seg 1 --> D;
  then product <*D*> = Funcs(Seg 1,D) by CARD_3:11;
  hence thesis by FINSEQ_2:93;
end;
