reserve m, n for Nat;

theorem Th34:
  for p being Prime holds Moebius p = -1
proof
  let p be Prime;
  reconsider p1 = p as prime Element of NAT by ORDINAL1:def 12;
  Moebius p = (-1) |^ card support ppf p1 by Def3
    .= (-1) |^ card {p} by Th8
    .= (-1) |^ 1 by CARD_1:30;
  hence thesis;
end;
