@article{ITA_2001__35_4_367_0,
     author = {Cintioli, Patrizio and Silvestri, Riccardo},
     title = {The helping hierarchy},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {367--377},
     publisher = {EDP-Sciences},
     volume = {35},
     number = {4},
     year = {2001},
     mrnumber = {1880805},
     zbl = {1052.68050},
     language = {en},
     url = {http://www.numdam.org/item/ITA_2001__35_4_367_0/}
}