Definition: Collision sets; transcribed

For each inventory graph, let $y$ be its interaction vertex and let $x,u,v$ denote its displayed observable vertices when present. For a connected vertex subset $I$ containing $y$, with $|I|\ge 2$,

Intersections and loci obtained after contracting such subsets are included. Diagonals involving only a pre-existing observable subgraph retain their inherited normalization.