English: Assume a black figure is in the (bright green) center square. All dark green squares are locations where, if a black piece is on them, white can fork the two black pieces with a knight (i.e. there is at least one square on which white can place a knight to fork both pieces). All red squares are "safe" squares for black/"not forkable" squares for white (i.e. given the red square, there is no square where white can place a knight to fork both black pieces).

Generally, two "forkable" squares must be of the same color. However, there are two cases where this criterion is insufficient. Both cases are marked with red squares and exclamation marks. These are: 1. The second piece is two squares away, diagonally. 2. The second piece is four squares away, diagonally.

Chess pieces rendered by en:User:Cburnett, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons. Remainder created by myself.