We study EP, the subclass of NP consisting of those
languages accepted by NP machines that when they accept always have a
number of accepting paths that is a power of two. We show that the
negation equivalence problem for OBDDs (ordered binary decision
diagrams) ... more >>>

Is there an NP function that, when given a satisfiable formula
as input, outputs one satisfying assignment uniquely? That is, can a
nondeterministic function cull just one satisfying assignment from a
possibly exponentially large collection of assignments? We show that if
there is such a nondeterministic function, then the polynomial ... more >>>