@MartinSleziak Indeed it seems that
trigonometric-sums is a method from analytic number theory, and is frequently used in questions about trigonometric functions, often highly off-topic (not this one). The main problem is the absence of a tag excerpt.
Suppose I have a functor $f\colon C\to D$ between $\infty$-categories (I'll assume $C$ and $D$ are small.) Then I can form the slice categories and restriction functors
$$
D_{f/}\to D\qquad \text{and} \qquad D_{/f}\to D.
$$
These maps are left fibrations and right fibrations, respectively. By t...
