1) What is the supreme of sequence ?
2) What is the undermost of sequence ?
The supremum is the least upper bound. In other words, it is the smallest number greater than or equal to all elements of the sequence.
The infimum is the greatest lower bound. In other words, it is the largest number less than or equal to all elements of the sequence.
I've never heard the term undermost used before.
Is that what you were looking for?