Discretisation in algebraic $K$-theory of independent ample groupoids and their Steinberg algebras

Abstract

An independent ample groupoid $G$ comes equipped with a discrete groupoid $G_d$ and a proper étale correspondence $Ω:G_d\to G$. Discretisation with respect to a homological invariant $\mathcal{H}$ holds when $\mathcal{H}(Ω)$ is an equivalence. We show for example that discretisation with respect to the $K$-theory spectrum $\mathbb{K} \mathfrak{B}_G$ of the permutative category of bisections always holds, establish excision and continuity for this invariant, and use all this and explicit resolutions by independent groupoids to compute it for several families of ample groupoids. We also prove discretisation with respect to invariants of the Steinberg algebra $\ell[G]$ such as (homotopy) algebraic $K$-theory in several particular cases, and carry out computations.