ZFC counterexamples to Marstrand’s projection theorem
Establish whether a counterexample to conclusion (1) of Marstrand’s Projection Theorem, namely a set whose projections fail to have the expected Hausdorff dimension for almost every direction, can be constructed within ZFC without additional set-theoretic assumptions.
References
It remains open whether any counterexamples of this sort can be built within ZFC.
— Hyperarithmetic directions can all be exceptional for Marstrand's projection theorem
(2608.26904 - Greenberg et al., 27 Aug 2026) in Section 1, Introduction
Is there a Davies example provably in ZFC?
— Open Problems in Mathematical Logic
(2608.26628 - Barmpalias et al., 27 Aug 2026) in Section 7