On Curvature Expansion of Higher Spin Gauge Theory
  We examine the curvature expansion of a the field equations of a four-dimensional higher spin gauge theory extension of anti-de Sitter gravity. The theory contains massless particles of spin 0,2,4,... that arise in the symmetric product of two spin 0 singletons. We cast the curvature expansion into manifestly covariant form and elucidate the structure of the equations and observe a significant simplification. 
E. Sezgin and P. Sundell