# Spectral characterization of a graph on the flags of the eleven point biplane

A. Blokhuis, A.E. Brouwer

We characterize a 55-point graph by its spectrum $4^1, (-2)^{10}, (-1 \pm \sqrt{3})^{10}, ((3 \pm \sqrt{5})/2)^{12}$. No interlacing is used: examination of tr A^m for m = 7 together with study of the representation in the eigenspace for the eigenvalue -2 suffices.