https://books.google.com/books?id=0xACg6Z6T6wC&pg=RA1-PA76 page 76 At this point, it may be useful to refer to a word that has been used in connection with earlier examples. The King has been said to indulge in a process called Triangulation. The word is harder than the idea. The basic fact is that the King can move to an adjacent square in one move, two moves or three moves, without returning to its point of origin. […] https://books.google.com/books?id=0xACg6Z6T6wC&pg=RA1-PA77 page 77 This diagram […] shows a position where the triangulation is vital.