( 1)

S has the minimum number S, then S is the lowest supremum.

(2)

S has no minimum number, isn't it familiar? It looks like s>a, but s≠a looks like it.

Then the division of s A/B makes

The lower bound of s belongs to a, and the rest belongs to B.

Then the maximum number of b is the lower bound of a.

Do the same thing for another problem.