A canonical bracket for open gravitational system

This paper shows that the generalization of the Barnich-Troessaert bracket recently proposed to represent the extended corner algebra can be obtained as the canonical bracket for an extended gravitational Lagrangian. This extension effectively allows one to reabsorb the symplectic flux into the dressing of the Lagrangian by an embedding field. It also implies that the canonical Poisson bracket of charges forms a representation of the extended corner symmetry algebra.