Draw a map of an underground of a city (with horizontally and vertically lines from center to center of the fields). Note:
- At the center of a field, the lines may turn or branch.
- The whole map is connected.
- There are no dead ends.
- The underground cannot leave the grid.
- The numbers at the borders give the corresponding numbers in that row or column. The pieces may be rotated.
- Fields may stay empty.