@article{ITA_1980__14_4_349_0,
     author = {Culik II, K. and Karhum\"aki, J.},
     title = {On the equality sets for homomorphisms on free monoids with two generators},
     journal = {RAIRO. Informatique th\'eorique},
     pages = {349--369},
     publisher = {EDP-Sciences},
     volume = {14},
     number = {4},
     year = {1980},
     mrnumber = {607436},
     zbl = {0454.20048},
     language = {en},
     url = {http://archive.numdam.org/item/ITA_1980__14_4_349_0/}
}