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3 votes

Is there an ∞-categorical interpretation of the Quillen S⁻¹S construction?

Consider an $E_n$-monoid X. We can deloop $X$ to an $\infty$-category $\mathbf{B}X$. There's a natural functor $X^\circlearrowleft : \mathbf{B}X \rightarrow \text{Spc}$ given by the left action of $X$ …
Georg Lehner's user avatar
  • 2,303
8 votes
0 answers
120 views

The homotopy inverse on Quillen's $S^{-1}S$ construction

Suppose $S$ is a symmetric monoidal groupoid. Take Quillen and Grayson's $S^{-1}S$-construction, which is a symmetric monoidal category with objects given by pairs $(m,n)$ and maps given by compositio …
Georg Lehner's user avatar
  • 2,303
4 votes
0 answers
92 views

How to describe a concrete generator of $\widetilde{K_0(\mathbb{Z}[C_{23}])} \cong \widetild...

Milnor (page 29, see below) gives an explicit proof that the zeroth $K$-theory of the group ring $\mathbb{Z}[C_p]$, where $C_p$ is the cyclic group of order $p$ with $p$ a prime agrees with $K_0$ of $ …
Georg Lehner's user avatar
  • 2,303
4 votes
1 answer
170 views

Injectivity of assembly in A-theory for $BC_2 = \mathbb R P^\infty$ in degree $4$

I am trying to understand the assembly map $$\pi_i ((BC_2)_+ \wedge A( \ast )) \rightarrow A_i( BC_2 ) $$ in low degrees for the space $BC_2 = \mathbb R P^\infty$ in Waldhausen $A$-theory. I know we h …
Georg Lehner's user avatar
  • 2,303
8 votes
1 answer
242 views

Finite group such that $K_{-1} (\mathbb Z G)$ has non-trivial torsion

According to Carters Lower K-theory of finite groups for a finite group $G$ we have $$ K_{-1} (\mathbb Z G) = \mathbb Z^r \oplus \mathbb Z_2^s $$ where $s$ is the sum over all irreducible representati …
Georg Lehner's user avatar
  • 2,303