Author: Andrey Bogdanov
Divide the grid following the grid lines so that each part contains all letters (A,B,C,D) exactly once.
Grid control: To draw a cut click at the cell edge or move mouse along the line holding the button. You can also connect the centers of cells which belong to the same part with auxiliary line. In this case cut lines will be added automatically. More details about grid control are at the help page.