@article{DMTCS_2010_12_4_a0,
     author = {Almeida, Jorge and Klima, Ondrej},
     title = {New decidable upper bound of the second level in the {Straubing-Therien} concatenation hierarchy of star-free languages},
     journal = {Discrete mathematics & theoretical computer science},
     publisher = {mathdoc},
     volume = {12},
     number = {4},
     year = {2010},
     doi = {10.46298/dmtcs.490},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.46298/dmtcs.490/}
}