Aha. For each side of the pole, you can write the binary representation of 4 bits vertically, and where there’s a 1 you have a line joining it. The middle two bits both go to the middle of the pole, so they have to curve off upward or downward to indicate which they are.
So 2 is 0010, and you have no lines in the top half and one line representing the bottom of the middle, so it curves downward.
Whereas 4 is 0100, so it has the upward-curving middle-connecting line, and none in the bottom half.
Aha. For each side of the pole, you can write the binary representation of 4 bits vertically, and where there’s a 1 you have a line joining it. The middle two bits both go to the middle of the pole, so they have to curve off upward or downward to indicate which they are.
So 2 is 0010, and you have no lines in the top half and one line representing the bottom of the middle, so it curves downward.
Whereas 4 is 0100, so it has the upward-curving middle-connecting line, and none in the bottom half.