The Laplacian $S_{n,n}$ conjecture is true

The “$S_{n,n}$ conjecture” asserts that there does not exist a simple graph on $n$ vertices with Laplacian spectrum $\{0,1,2,\dots ,n-1\}$ for any integer $n\ge 2$. This conjecture has already been proved when $2\le n\le 15$ and when $n\ge 6,649,688,933$. We prove all remaining cases and thus establish that the conjecture is true.