  We propose to apply the two-particle irreducible (2PI) formalism to the
problem of thermalization in heavy-ion collisions in the Color Glass Condensate
(CGC) picture. We consider the 2PI effective action to three loops and derive a
set of coupled equations for the classical Yang-Mills field and the quantum
fluctuations in the boost invariant coordinate system. The initial condition
and the relation to previous works are also discussed.
