@article{DBLP:journals/tcs/Straubing88,
author = {Howard Straubing},
title = {Semigroups and Languages of Dot-Depth Two},
journal = {Theor. Comput. Sci.},
volume = {58},
year = {1988},
pages = {361-378},
ee = {http://dx.doi.org/10.1016/0304-3975(88)90034-5},
bibsource = {DBLP, http://dblp.uni-trier.de}
}