no. 2
How much semigroup structure is needed to encode graphs ?
RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 20 (1986) no. 2, pp. 191-206. 
@article{ITA_1986__20_2_191_0,
     author = {Goral\v{c}{\'\i}k, P. and Goral\v{c}{\'\i}kov\'a, A. and Koubek, V.},
     title = {How much semigroup structure is needed to encode graphs ?},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {191--206},
     publisher = {AFCET - Gauthier-Villars},
     address = {Paris},
     volume = {20},
     number = {2},
     year = {1986},
     mrnumber = {860769},
     zbl = {0601.20053},
     language = {en},
     url = {http://archive.numdam.org/item/ITA_1986__20_2_191_0/}
}
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Goralčík, P.; Goralčíková, A.; Koubek, V. How much semigroup structure is needed to encode graphs ?. RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 20 (1986) no. 2, pp. 191-206. http://archive.numdam.org/item/ITA_1986__20_2_191_0/

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