
theorem
  for L being positive-definite Z_Lattice, v being Vector of L holds
  ||. v .|| >= 0
  proof
    let L be positive-definite Z_Lattice, v be Vector of L;
    per cases;
    suppose v = 0.L;
      hence thesis by ThSc6;
    end;
    suppose v <> 0.L;
      hence thesis by defPositive;
    end;
  end;
