Coming in the other direction, the soldiers looked exactly like the Ukrainian unit walking out of Pokrovsk after a 15-day deployment.They wore the same blue armbands and carried the same equipment. One of the four men said “hello”.But minutes later, a warning came over the radio: “Be careful, there is a group of Russian infiltrators in your area.”“We passed right by them,” says Ivan, a 21-year-old machine gunner in an unmanned systems unit from the Da Vinci Wolves. “The men I saw matched the description exactly.”Inside Pokrovsk, the dividing lines of urban warfare have faded. In their place is a...