Lane A. Hemaspaandra Ashish V. Naik Mitsunori Ogihara Alan L. Selman Computing Solutions Uniquely collapses the Polynomial Hierarchy. 56-64 1994 conf/isaac/1994 ISAAC db/conf/isaac/isaac94.html#HemaspaandraNOS94 http://dx.doi.org/10.1007/3-540-58325-4_166