The area inhabited by the Sorbs corresponds roughly to the regions ofUpper Lusatia (Oberlausitz) for Upper Sorbian and Lower Lusatia (Niederlausitz) for Lower Sorbian. At present, this area covers appr.95km in its north/south expansion, and appr. 60km in its widest west/east expansion. According to recent statistics (1991), the number of Upper Sorbian speakers does not exceed 53,600, a 44% reduction since the mid 1880s (by comparison, Lower Sorbian declined by 81% in the same period). Upper Sorbian is classified as belonging to the WestSlavic group of languages. However, Upper Sorbian (like Lower Sorbian) has a number of linguistic features that are not found in any of the other members of that group: it has retained the Old Slavic tense system with aorist, imperfect, and perfect past tenses. In many dialects, the dual number is marked for both nominals and verbals. Centuries of contact with German have left an indelible imprint, especially on colloquial Upper Sorbian and on dialects. TheUpper Sorbian language area, small as it is, is divided into at least nine major dialects. There are, in addition, many regional dialects. Politically, Upper Sorbian is part of Saxony ("FreistaatSachsen"). The German Unity Treaty of 1990 guarantees the rights ofSorbian speakers to use their language in the public domain and in the courts in the Sorbian-speaking areas.