theorem Th16:
  for x being object holds
  for E be Enumeration of Av holds len (x|--E) = card Av
proof let x be object;
  let E be Enumeration of Av;
  rng E=Av by Def1;
  then len E=card Av by FINSEQ_4:62;
  hence thesis by FINSEQ_2:33;
 end;
