  If two classical provers share an entangled state, the resulting interactive
proof system is significantly weakened [quant-ph/0404076]. We show that for the
case where the verifier computes the XOR of two binary answers, the resulting
proof system is in fact no more powerful than a system based on a single
quantum prover: +MIP*[2] is contained in QIP(2). This also implies that
+MIP*[2] is contained in EXP which was previously shown using a different
method [Presentation of Cleve et al. at CCC'04]. This contrasts with an
interactive proof system where the two provers do not share entanglement. In
that case, +MIP[2] = NEXP for certain soundness and completeness parameters
[quant-ph/0404076].
