@book{Gratzer,
  author = {Gr\"atzer, George},
  edition = {2.},
  interhash = {a8f3bffb2e67cba1f5e527baf3d52c5c},
  intrahash = {d83a5bf84d8f9a73cfbdf029cf77bd00},
  publisher = {Birkh\"auser Verlag},
  title = {General Lattice Theory},
  year = 1998
}