two requirements need to be met at the same time:

1 and a should be less than or equal to the potential of the corresponding element in b. There is at least one element f in
2 and b, whose potential is greater than that of the corresponding element in a.

the meaning of Article 1 is more intuitive, while the meaning of Article 2 may not be easy to understand at first glance. Here is a brief explanation.

Article 1 requires that the potential of the element in an is less than or equal to the potential of the element in b, while Article 2 requires that the potential of the element in a cannot be equal to the potential of the element in b, but there must be at least one less than before it can be called "proper subcollection".