Arto Salomaa Subword Balance in BinaryWords, Languages and Sequences. 469-482 2007 75 Fundam. Inform. 1-4 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=75&issue=4&spage=469 db/journals/fuin/fuin75.html#Salomaa07