@article{ITA_2006__40_4_551_0,
     author = {Halava, Vesa and Harju, Tero},
     title = {Undecidability of infinite post correspondence problem for instances of size 9},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {551--557},
     publisher = {EDP-Sciences},
     volume = {40},
     number = {4},
     year = {2006},
     doi = {10.1051/ita:2006039},
     mrnumber = {2277048},
     zbl = {1114.03035},
     language = {en},
     url = {http://www.numdam.org/articles/10.1051/ita:2006039/}
}