Hjorth–Kechris dichotomy conjecture for Borel equivalence relations

Let EE be a Borel equivalence relation, and let E1E_1 denote eventual agreement on countable sequences of reals. For equivalence relations EE and FF, write EBFE\leq_B F when EE is Borel reducible to FF, and say that they are Borel bireducible when each is Borel reducible to the other. An orbit equivalence relation is the equivalence relation induced by a Borel action of a Polish group. Hjorth–Kechris conjecture. Either E1BEE_1\leq_B E or EE is Borel bireducible with an orbit equivalence relation. This is a proposed dichotomy for Borel equivalence relations, refining the obstruction given by E1E_1. The analogous Kechris–Louveau dichotomy is known in restricted settings but is false in general; the Hjorth–Kechris version is presented as a conjecture and its status is not resolved in the supplied text.

Sources & referencesView supporting material

Primary source

Filippo Calderoni and Luca Motto Ros, “Structural results on idealistic equivalence relations”, arXiv:2506.08217 (2025).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.