closed 2-forms. The fact that is a stack is a first step towards a deeper understanding of what it means to restore the continuity of composition using derived geometry.

Moreover, the second issue - the failure of composition to be continuous - is closely related to the failure to quantize classical mechanics functorially: After quantizing pairs where the composite fails to depend continuously on $L$ and $L'$, one is typically trying to multiply Dirac $\delta$-functions in the corresponding quantization. In work in progress with Gwilliam, Haugseng, Johnson-Freyd, Scheimbauer, and Weinstein, we show that *at least to first order* (i.e. after linearizing),

-   the *derived* composition of Lagrangian correspondences depends continuously on $L$ and $L'$ (cf. [@LiBland:2014tf]), and

-   there is a functorial quantization.

In order to show that and define stacks, we first need to examine limits of $\infty$-categories. Suppose that ${\mathcal}{C}_k,\quad k\in K$ is some diagram of $\infty$-categories indexed by a simplicial set $K$. In [@Riehl:2014ut], Riehl and Verity show that if each ${\mathcal}{C}_k$ has all (co)limits of shape $I$ (where $I$ is some small simplicial set), and for each arrow $k\to k'$ in $K$, the corresponding functor ${\mathcal}{C}_k\to {\mathcal}{C}_{k'}$ preserves all (co)limits of shape $I$, then the limit 