  Tsuzuki has conjectured that for crystals with Frobenius and connection over
a local field k((t)), the embedding of the category of overconvergent crystals
into the category of convergent crystals is fully faithful. We prove Tsuzuki's
conjecture restricted to the subcategory of potentially semistable (or
quasi-unipotent) crystals, following de Jong's proof of a slightly weaker
result. We also prove Tsuzuki's conjecture restricted to crystals with at most
two distinct slopes.
