@misc {IOPORT.70297808,
    author       = {Pol\'ak, Libor},
    title        = {On pseudovarieties of semiring homomorphisms},
    howpublished = {MFCS, 635-647 (2004).},
    year         = {2004},
    doi          = {10.1007/978-3-540-28629-5_49},
    identifier   = {70297808},
}