A variation δ δ u σ σ = X σ σ ( x , u , u ( 1 ) , … … ) is an infinitesimal symmetry of the Lagrangian L if δ δ L = 0 under this variation. It is an infinitesimal quasi-symmetry if there is a current K i = K i ( x , u , … … ) such that δ δ L = d i K i .