  This paper proves that classical-witness quantum Merlin-Arthur proof systems
can achieve perfect completeness. That is, QCMA = QCMA1. This holds under any
gate set with which the Hadamard and arbitrary classical reversible
transformations can be exactly implemented, e.g., {Hadamard, Toffoli, NOT}. The
proof is quantumly nonrelativizing, and uses a simple but novel quantum
technique that additively adjusts the success probability, which may be of
independent interest.
