Before revision:  Our proposal uses a sub-optimal MAPF solver to obtain an initial solution quickly, then iterates the two procedures: 1)  select a subset of agents, 2)  use an optimal MAPF solver to refine paths of selected agents while keeping other paths unchanged.
After revision:  Our proposal uses a sub-optimal MAPF solver to obtain an initial solution quickly, then iterates the two procedures: 1) ~ select a subset of agents, 2) use an optimal MAPF solver to refine paths of selected agents while keeping other paths unchanged.