Comparative strength of Second-order Absolute Morley variants
Determine whether the principle stating that if E is an equivalence relation on R that is a countable intersection of projective sets and there is no perfect set of pairwise E-inequivalent reals, then E has at most aleph_1 equivalence classes, is strictly weaker than the corresponding principle for sigma-projective equivalence relations.
References
We do not know if Second-order Absolute Morley for countable intersections of projective sets is strictly weaker than Second-order Absolute Morley for $\sigma$-projective equivalence relations.
— The Second-order Version of Morley's Theorem on the Number of Countable Models does not Require Large Cardinals
(2401.10454 - Tall et al., 19 Jan 2024) in Introduction