@article{ITA_1990__24_3_267_0,
     author = {Engelfriet, Joost and Leih, George},
     title = {Complexity of boundary graph languages},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {267--274},
     publisher = {EDP-Sciences},
     volume = {24},
     number = {3},
     year = {1990},
     mrnumber = {1072994},
     zbl = {0701.68062},
     language = {en},
     url = {http://www.numdam.org/item/ITA_1990__24_3_267_0/}
}