Uniqueness of six-functor formalisms

Abstract: We present an alternative formulation of Scholze's notions of cohomologically proper and cohomologically \'etale with respect to an abstract six-functor formalism. These conditions guarantee canonical isomorphisms between the direct and exceptional direct images for certain "proper" morphisms, and between the inverse and exceptional inverse images for certain "\'etale" morphisms. Using this framework, we prove Scholze's conjecture, showing that a six-functor formalism with sufficiently many cohomologically proper and \'etale morphisms is uniquely determined by the tensor product and inverse image functors, and can be obtained by a construction of Liu-Zheng and Mann. Additionally, we show that a generalisation of the conjecture fails, and propose a measure of this failure in terms of K-theory.