aaaa aaab aaas aaba aabb aabt aasa aass aast aata aatt abaa abab abas abat abb- abba abbb abbs abbt abs- absa abss abta abts asaa asab asas asat asba assa asss asst asta astb asts at-t ataa atab atas atat atbs atsb atst atta atts baaa baas baat baba babb babs basa bass bast bata bats batt bbas bbbb bbbs bsaa bsas bsat bsts btaa btss bttb saab saas saat saba sabb sabs sasa sass sast sata satb sats satt sbaa sbas sbbs sbsa sbst ssaa ssab ssas ssat sssa sssb ssss ssta sstb ssts stab stas stat stbs stss taa- taas taat taba tabb tabs tasa tasb tass tast tata tatb tats tatt tbas tbbs tbst tbta tsaa tsat tssa tsst tsts ttab ttbb ttss tttt