@Article{KR73,
  author = 	 { David A. Klarner and Ronald L. Rivest },
  title = 	 { A procedure for improving the upper bound for the number of N-ominoes },
  journal = 	 { Canadian Journal of Math. },
  OPTyear = 	 { 1973 },
  OPTmonth = 	 { June },
  date =         { 1973-06 },                  
  volume = 	 { 25 },
  number =       { 3 },                    
  pages = 	 { 585--602 },
  doi =          { 10.4153/CJM-1973-060-4 },                    
}