  We introduce twisted differential calculus of negative level and prove a
descent theorem: Frobenius pullback provides an equivalence between finitely
presented modules endowed with a topologically quasi-nilpotent twisted
connection of level minus one and those of level zero. We explain how this is
related to the existence of a Cartier operator on prismatic crystals. For the
sake of readability, we limit ourselves to the case of dimension one.
