@unpublished{Ho2014c,
  title = "The UAV Problem is PSPACE-Complete",
  author = "Ho, Hsi-Ming and Ouaknine, Jo\"{e}l",
  year = "2014",
  note = "Submitted.",
  url = "http://www.cs.ox.ac.uk/people/hsi-ming.ho/UAV14.pdf",
}