For each "time-step" δ δ , e − − i δ δ 2 F [ l ] are applied successively to all odd sites, then e − − i δ δ G [ l ] to the even ones, and e − − i δ δ 2 F [ l ] again to the odd ones; this is basically a sequence of TQG's, and it has been explained above how to update the decomposition D when applying them.