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Underground (1140)
Other names: U-Bahn
Instruction:
Draw orthogonal connections through centers of cells to form one connected network. It is not allowed to have any cell with only one connection. It is allowed for any cell to have no connections; fill them with an X-shaped cross. Each cell with connections will therefore be one of these four types: connected to two cells at right angles, two cells in a line, three cells, or four cells. The numbers above and to the left of the grid indicate the exact number of cells of the specified type that must be placed in each column or row, respectively. If a number is not given, there might be any number of cells of the specified type. The contents of some cells may be given to you; any such cell has all of its connections given.