@article{Drzewiński:1991,
  author  = "A. Drzewiński and J. Sznajd",
  title   = "On the real-space renormalization-group study of some 2D quantum spin systems",
  journal = "Physica A",
  volume  = "Vol. 170",
  pages   = "415--438",
  year    = "1991",
}