Could you elaborate on ECPP false negatives? A properly working ECPP should never give false negatives, e.g. return "prime" for a composite. Since ECPP can gi

Could you elaborate on ECPP false negatives? A properly working ECPP should never give false negatives, e.g. return "prime" for a composite. Since ECPP can give a certificate unlike AKS or APR-CL, the caller could do a relatively quick check of the math. Some proof methods: - BPSW. Deterministic, completely correct for all 64-bit values. Purely a compositeness test above, though no counterexamples known. This matches the false-positive idea -- above 64-bit it returns one of "definitely composite" or "probably prime." - BLS 1975 methods. Relies on partial factoring N-1 and/or N+1 so unless the input is a special form, only practical to ~100 digits. No false results if the partial factoring can be done, and even gives a certificate of primality. - APR-CL. Deterministic. No false results. Fast and practical up to ~5000 digits (one can debate where the impractical size line is). No certificate. - AKS. Deterministic. No certificate. No false results. Very slow, so not generally used. - ECPP. Non-deterministic (randomness is used internally), but no false results. Generates a certificate. Primo is practical up to ~30k digits (depends on your hardware and patience, but 10k digits on modern computers is quite practical). Open source implementations aren't as efficient, but still 1k+ digits is very reasonable. It is possible an implementation might be unable to proceed for various reasons and could return "gave up - no primality decision made" in addition to the choices "definitely composite" or "definitely prime (certificate included)". That's really a limitation of the implementation or the caller's patience.