The class of decision problems solvable by an NP machine such that
Significantly, the number of candidate witnesses is restricted to be a power of 2. (This is implicit if they are binary strings.)
Contained in RP, EP, and ModkP for every odd k. Contained in EQP by the Deutsch-Jozsa algorithm.
Defined in [BB92], where it was called C==P[half] (C==P being an alternative name for WPP, that apparently didn't catch on or stick). The name used here is from [BS00]. There it was shown that HalfP is contained in every similar class in which 1/2 is replaced by some other dyadic fraction.
No class.