reserve m, n for Nat;

theorem Th33:
  for n being Nat st n is square-free holds Moebius n <> 0
proof
  let n be Nat;
  assume n is square-free;
  then consider n9 being non zero Nat such that
A1:  n9 = n & Moebius n = (-1) |^ card support ppf n9 by Def3;
   Moebius n = (-1) |^ card support ppf n9 by A1;
  hence thesis by CARD_4:3;
end;
