@article{BS-Kybernetika,
 author = {Andrej Bebják and Ivana Štefáneková},
 journal = {Kybernetika},
 pages = {65 - 71},
 title = {Nondeterminism is essential for reversal-bounded two-way 
multihead finite automata},
 volume = {24},
 year = {1988}
}