The class of decision problems that have PZK protocols assuming an honest verifier (i.e. one who doesn't try to learn more about the problem by deviating from the protocol).
Contained in PP [BHCTV17].There is an oracle where it is not closed under complement [BHCTV17].
Same as SZK, but now the two distributions must be identical, not merely statistically close. (The "two distributions" are (1) the distribution over the verifier's view of his interaction with the prover, conditioned on the verifier's random coins, and (2) the distribution over views that the verifier can simulate without the prover's help.)
Contained in SZK and HVPZK.There are oracles separating PZK from SZK, coPZK, NIPZK, and coSBP. [BCHTV17], [DGPV20].
See also: CZK.