Suppose an oracle is known to hold one of a given set of D two-valued
functions. To successfully identify which function the oracle holds with k
classical queries, it must be the case that D is at most 2^k. In this paper we
derive a bound for how many functions can be distinguished with k quantum
queries.Comment: 5 pages. Lower bound on sorting n items improved to (1-epsilon)n
quantum queries. Minor changes to text and corrections to reference
