I have tried to count the number of simple labelled bipartite graphs $G_{n,m}$ with $k$ edges such that $d_1$ vertices have degree 1.
Has this problem been studied?
So far the only related paper I found shows a generating function to count all simple labelled graphs where monovalent vertices are represented by u:
$M(u,x) = \sum_{k \geq 0} \frac{x^k}{k!}2^{{k\choose 2}}(e^{ux})^{k}e^{u^2x^2/2}$
This paper also has some results on bipartite graphs, but as I'm not familiar with generating functions, I don't know how to adapt these results to my original problem. Any help would be appreciated.