A Spanning Subgraph of Conway's 99-graph

Abstract

We show that in any hypothetical $G$ = srg(99,14,1,2) a spanning subgraph with $189$ edges is forced. Moreover, the graph formed out of the remaining edges has the spectrum $(12^1,-4^{30},3^{40},-2^6,0^7)$ expressed in Brouwer's notation.

arXiv comment4 pages, 2 figures. v2: Substantially reworked, though the overarching topic remains the same