v . . . .v .v . # x . # ### #### #.. . . ... ..# # .. . #...##.∩## . . # .#...#§#.# . # . #....# .# . .#....#### .. ##.XX#....... . #.#........#.. ##...XXX#..#...### #...X.X. #.#..# #..##....# ##### ### ##..#.# ...#... ..###. #.. #.