José L. Balcázar Ronald V. Book Timothy J. Long Uwe Schöning Alan L. Selman 308-311 conf/focs/FOCS25 1984 FOCS db/conf/focs/focs84.html#BalcazarBLSS84 http://doi.ieeecomputersociety.org/10.1109/SFCS.1984.715929