- #1
Mr Davis 97
- 1,462
- 44
Given that ##A## is a nonempty set of real numbers, and that ##-A = \{-x ~ | ~ x \in A\}##, I want to show the following:
##\forall a' \in -A, ~ \sup (-A) \ge a'## implies that ##\forall a \in A, ~\sup (-A) \ge -a##.
This is intuitively obvious, as we just "replace" ##a'## with ##-a##. But I don't see how to make the switch from one to the other rigorously.
##\forall a' \in -A, ~ \sup (-A) \ge a'## implies that ##\forall a \in A, ~\sup (-A) \ge -a##.
This is intuitively obvious, as we just "replace" ##a'## with ##-a##. But I don't see how to make the switch from one to the other rigorously.