Real analysis - proof approach help I am taking a course in Real Analysis this semester and thought I would work ahead a little bit.
I am just reading for the moment, but came across an interesting exercise, and was wondering if I could see how one of you would solve it.
Assume that $A$ and $B$ are nonempty, bounded above, and satisfy $B⊆A$. Show $\sup B≤\sup A.$
Not so much that the question perplexes me, but rather I wanted to see an example of a rigorous proof for this question.

Hint: Can you show that $\sup A$ is an upper bound for $B$?
