Move of Knight

It may most likely be the information long known by skilled chess players, but I am writing it because I am quite happy that I was able to discover it.

You want to move your #knight from square (x1 y1) to square (x2 y2). If x1-x2+y1-y2 ≠ 3N (N = a natural number), you must move the knight backwards, i.e. in the opposite direction to the targeted square, at least once.

#Chess