2
$\begingroup$

By Deligne-Illusie, such a variety has no lifting to $W_2(k)$. In their paper they state that they do not know if such an example exists. Has this question been answered since then?

$\endgroup$
  • 4
    $\begingroup$ Search for "exceptional Enriques surfaces". $\endgroup$ – Jason Starr 2 days ago
  • 4
    $\begingroup$ Deligne-Illusie do not claim that; in fact they cite Mumford's paper "Pathologies of modular surfaces" for a counterexample. What they say they don't know is whether the assumption $p>\dim X$ in their theorem is necessary; that is, whether there exists a variety liftable to $W_2(k)$, necessarily of dimension $\leq p$, for which the Hodge-de Rham spectral sequence does not degenerate. This is an open problem, to the best of my knowledge. $\endgroup$ – Piotr Achinger 2 days ago
  • $\begingroup$ @PiotrAchinger You are right. I misread that paragraph. I assume you mean $\dim > p$, in any case. $\endgroup$ – Kim 2 days ago

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.