@article{eprints319,
       publisher = {Elsevier},
          number = {1-3},
           pages = {179--189},
         journal = {Theoretical Computer Science},
           title = {Nondeterministic regular expressions as solutions of equational systems},
          author = {Rocco De Nicola and Anna Labella},
            year = {2003},
          volume = {302},
             url = {http://eprints.imtlucca.it/319/},
        abstract = {We define the class of the linear systems whose solution is expressible as a tuple of nondeterministic regular expressions when they are interpreted as trees of actions rather than as sets of sequences. We precisely characterize those systems that have a regular expression as "canonical" solution, and show that any regular expression can be obtained as a canonical solution of a system of the defined class.}
}