asahui

                    +--[■]---->+----[■]----+
                    |          |           |
         +---[■]--->+          |           |
         |          |          |           |
  [■]--->+          +--[■]---->+----[■]----+-->[■]-->--[■]
         |          |          |           |
         +---[■]--->+          |           |
                    |          |           |
                    +--[■]---->+----[■]----+