Expansion of Building-Like Complexes
  Following Gromov, the coboundary expansion of building-like complexes is studied. In particular, it is shown that for any $n \geq 1$, there exists a constant $\epsilon(n)>0$ such that for any $0 \leq k <n$ the $k$-th coboundary expansion constant of any $n$-dimensional spherical building is at least $\epsilon(n)$. 
Alexander Lubotzky, Roy Meshulam, Shahar Mozes
math.CO math.GR