The largest element and the smallest element are complementary. When seeking the complement of other elements, if A and B are complementary, then the path from these two points only intersects with the largest element upward and only intersects with the smallest element downward. Here b and c, b and d can all be like this.

On the right, b and c, b and d, c and d also satisfy this point.

For finite set b, the minimal element must exist, but the minimal element does not necessarily exist. If the smallest element exists, it must be unique, but there may be multiple smallest elements.

Extended data:

The largest element that is easy to get must be the largest element, but the largest element is not necessarily the largest element. Pay attention to the difference between the largest element and the largest element. ?

The largest element is the largest element in B, which is comparable to other elements in B; Maximal element is not necessarily comparable to all other elements in B, as long as there is no big element, it is maximal element. For finite set b, the maximal element must exist, but it does not necessarily exist. The maximum element, if it exists, must be unique, but there can be multiple maximum elements.