@article{helmert:etal:jacm-14,
  author =    {Malte Helmert and Patrik Haslum and J{\"o}rg Hoffmann and Raz Nissim},
  title =     {Merge \& Shrink Abstraction: A Method for Generating Lower Bounds in Factored State Spaces},
  journal   = jacm,
  year      = {2014},
  number = {3},
  volume = {61}
}

@STRING{jacm  = "Journal of the Association for Computing Machinery"}