Left lattice, A is the largest element and E is the smallest element. The largest element and the smallest element are complementary. When finding the complementary elements of other elements, if A and B are complementary, it can be seen from the figure that the path from these two points only intersects the element with the largest intersection upward and the element with the smallest intersection downward. Here, b and c, b and d can all do this.

Right case, b and c, b and d, c and d also satisfy this point.