
theorem
  for I being set, MSS being ManySortedSet of I holds MSS#.<*>I = {{}}
proof
  let I be set, MSS be ManySortedSet of I;
  reconsider eI = <*>I as Element of I* by FINSEQ_1:49;
  thus MSS#.<*>I = product (MSS*eI) by FINSEQ_2:def 5
    .= {{}} by CARD_3:10;
end;
