@INPROCEEDINGS{SchmittHedtstueck90,
        AUTHOR       = {Peter~H. Schmitt and U. Hedtst\"{u}ck},
        BOOKTITLE    = {Sorts and Types in Artificial Intelligence, 
                        Proc. of the Workshop, Ehringerfeld},
        EDITOR       = {U.~Hedst\"{u}ck, C.-R.~Rollinger, K.~H.~Bl\"{a}sius},
        PAGES        = {61--72},
        PUBLISHER    = {Springer Verlag},
        SERIES       = {Lecture Notes in AI},
        TITLE        = {A calculus for order-sorted predicate logic 
                        with sort literals},
        VOLUME       = {418},
        YEAR         = {1990}
}