As in the case of BPP, we can reduce the error probability of any MA protocol to be less than an inverse exponential in the input size. Here’s how. Let L ∈ MA be any language. Let R(x, y, z) be a polytime relation for L such that, for every x ∈ L, there is a y with Prz[R(x, y, z) = 1] ≥ 3/4; and for every x 6∈ L, for every y, it holds that Prz[R(x, y, z) = 1] ≤ 1/4. Consider a new protocol wher...