You are given a grid with several black cells. Fill every blank cell with a line, which connects two cell edges and goes horizontally or vertically through the center of the cell. The lines must follow these rules:
A line is connected to a black cell when it runs into it: a horizontal line in the cell to its left or right, or a vertical line in the cell above or below. A line lying alongside a black cell — a vertical line beside it, or a horizontal line above it — does not connect to it, and can never come to. That is why a black cell can run out of usable sides long before its number is met.
This puzzle type was invented by Nikoli, and is known as Tatebo-Yokobo.
More information: https://www.janko.at/Raetsel/Tateboo-Yokoboo/index.htm
To place a line, drag the mouse horizontally or vertically inside a cell.
To place a line without dragging the mouse, left-click to place a vertical line and right-click to place a horizontal line.
To play with a keyboard, use the arrow keys to move the cursor. Press Enter to place a vertical line, and press Space to place a horizontal line.
These parameters are available from the ‘Custom…’ option on the ‘Type’ menu.