Gradient expansion of superhorizon perturbations in G-inflation
  We develop the gradient expansion formalism for shift-symmetric Galileon-type
actions. We focus on backgrounds that undergo inflation, work in the
synchronous gauge, and obtain a general solution up to second order without
imposing extra conditions at first order. The solution simplifies during the
late stages of inflation. We also define a curvature perturbation conserved up
to first order.
