Abstract

We introduce a new formalism for $K$-theory, called squares $K$-theory. This formalism allows us to simultaneously generalize the usual three-term relation $[B]=[A]+[C]$ for an exact sequence $A\hookrightarrow B\twoheadrightarrow C$ or for a subtractive sequence $A\hookrightarrow B\leftarrow C$ by defining $K_0$ of a squares category to satisfy a four-term relation $[A]+[D]=[C]+[B]$ for a “good” square diagram with these corners. Examples that rely on this formalism are $K$-theory of smooth manifolds of a fixed dimension and $K$-theory of (smooth and) complete varieties. Another application we give of this theory is the construction of a derived motivic measure taking value in the $K$-theory of homotopy sheaves.

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