reserve i for Nat, x,y for set;
reserve S for non empty non void ManySortedSign;
reserve X for non-empty ManySortedSet of S;

theorem Th21:
  for a1,a2,a3,a4,a5,a6,a7,a8,a9 being object holds
  rng(<*a1,a2,a3,a4,a5,a6,a7,a8*>^<*a9*>) = {a1,a2,a3,a4,a5,a6,a7,a8,a9}
  proof
    let a1,a2,a3,a4,a5,a6,a7,a8,a9 be object;
    thus rng(<*a1,a2,a3,a4,a5,a6,a7,a8*>^<*a9*>)
    = rng <*a1,a2,a3,a4,a5,a6,a7,a8*> \/ rng <*a9*> by FINSEQ_1:31
    .= {a1,a2,a3,a4,a5,a6,a7,a8} \/ rng <*a9*> by Th20
    .= {a1,a2,a3,a4,a5,a6,a7,a8} \/ {a9} by FINSEQ_1:38
    .= {a1,a2,a3,a4,a5,a6,a7,a8,a9} by ENUMSET1:84;
  end;
