The types of triangles just considered are relatively easy to see once you know to look for them because they have a regular, almost equilateral appearance. But even the more oddly-shaped triangles can be found by habitually looking at what the bishop already attacks—the line of enemy pieces that lie ahead of it on any of the diagonals it commands, and what else it can attack by taking one of them. (See the diagram to the left, where the Black and White bishops each have a fork via a pawn capture that creates an unorthodox triangle.)
What does all this mean for practical play? It means you will want to scan the diagonals on the board—and the ranks and files, too—for pieces lined up on them. This is especially important when one of the pieces is a king. Also be alert for triangles, and relatedly for enemy pieces scattered about the board on the same color squares. A bishop can of course fork pieces only if they travel on the same color squares that it does; and almost any two enemy pieces on squares of the same color can, in principle, be forked by a bishop from some other square on the board—“almost” because there is no way to fork two pieces next to each other on the same diagonal. The general point nevertheless is useful, and reinforces a lesson from the chapter on knight forks: pieces on squares of the same color tend to be most vulnerable to double attacks of various kinds. Watch for them.
Now on to some examples.