Also known as:
Easy as ABC, Letterbox
The simplicity of the rules makes this a challenging and interesting little logical puzzle. It can be designed with various levels of difficulty. A particularly tricky version appeared for many years in 'Tough Puzzles' under the name Easy as ABC with a 6x6 grid and with an extra letter, D. The more common version uses a 5x5 grid and the letters A, B and C.
The best approach to solving the puzzle is to look for points where the clues for rows and columns appear to intersect, ie, seem to point at the same cells. Alternatively, a process of elimination can be used to discount those cells where letters can't possibly appear.
Enter the letters A to C into the grid so that each line, across and down, has each of the letters A, B and C, and two empty squares. The reference outside the grid indicates the first or second letter to appear in that row or column in the direction indicated by the arrow.