  In multi-prover interactive proofs (MIPs), the verifier is usually
non-adaptive. This stems from an implicit problem which we call
``contamination'' by the verifier. We make explicit the verifier contamination
problem, and identify a solution by constructing a generalization of the MIP
model. This new model quantifies non-locality as a new dimension in the
characterization of MIPs. A new property of zero-knowledge emerges naturally as
a result by also quantifying the non-locality of the simulator.
