
theorem
  for L being Z_Lattice, L1, L2 being Z_Sublattice of L holds
  0.L1 = 0.L2
  proof
    let L be Z_Lattice, L1, L2 be Z_Sublattice of L;
    thus 0.L1 = 0.L by defSublattice
    .= 0.L2 by defSublattice;
  end;
