Almost étale extensions of Fontaine rings and log-crystalline cohomology in the semi-stable reduction case
Let be a field of characteristic zero complete for a discrete valuation, with perfect residue field of characteristic , and let be the valuation ring of . We relate the log-crystalline cohomology of the special fibre of certain affine -schemes with good or semi-stable reduction to the Galois cohomology of the fundamental group of the geometric generic fibre with coefficients in a Fontaine ring constructed from . This is based on Faltings’ theory of almost étale extensions.