@article {IOPORT.05426594,
    author       = {Baeten, Jos C.M. and Corradini, Flavio and Grabmayer, Clemens},
    title        = {A characterization of regular expressions under bisimulation.},
    year         = {2007},
    journal      = {Journal of the ACM},
    volume       = {54},
    number       = {2},
    issn         = {0004-5411},
    publisher    = {Association for Computing Machinery (ACM), New York, NY},
    doi          = {10.1145/1219092.1219094},
    identifier   = {05426594},
}