@TechReport{pearl:12-r392,
  author = 	 "Pearl, J.",
  title = 	 "A note on the pairwise {Markov} condition in directed {Markov} fields",
  institution =  "Department of Computer Science, University of California, 
                  Los Angeles",
  address = 	 "CA",
  year = 	 2012,
  number =	 "R-392, {$<$http://ftp.cs.ucla.edu/pub/stat\_ser/r392.pdf$>$}"
}