Spahn relative nerve (Rev #1)

Let $J$ be a category, let $f:J\to (\infty,1)Cat\hookrightarrow sSet$ be a functor. Then there is a cocartesian fibration $p:N_f(J)\to N(J)$ which is related to $N(f)$ by the Grothendieck construction. $N_f(J)$ is called the relative nerve of $J$ relative $f$.

Let $L$ be a linear order. A map $\Delta^L\to N_f(J)$ consists of the following data:

(1) A functor $s:L\to J$.

(2) For every nonempty subset $L^\prime\subseteq L$ with maximal element $j^\prime\in L^\prime$, a map $t(J^\prime):\to \Delta^{L^\prime}\to f(s(j^\prime))$.

(3) Coherence in the obvious way: For nonempty subsets $L^{\prime \prime}\subseteq L^\prime\subseteq L$ with maximal elements $j^{\prime\prime}$ resp. $j^\prime$, the diagram

is required to commute.

References

• Jacob Lurie, Higher Topos Theory, §3.2.5

• Jacob Lurie, Derived Algebraic Geometry II, Noncommutative Algebra, §3.1, p.94-97

• The relative nerve appears en passant also in

  • Jacob Lurie, Higher Algebra, Construction 2.2.5.12

  • Jacob Lurie, $(\infty,2)$-Categories and the Goodwillie Calculus, Theorem 0.0.3 (B5)