As shown in figure A 1, A2 and A3 are equivalent, and B 1, B2 and B3 are equivalent, so we can see that the current is divided into 3, then divided into 2 for each 1, and finally merged. It can be seen that the current of each side is the same as that of its parallel diagonal side, and the flow direction is the same: for example, a1->; B3 and A3-& gt；; B 1，A-& gt； A 1 and b1->; B. so their magnetic fields cancel out at point o.