Does the intersection of two subsets (with a maximum) necessarily have a maximum too?

37 Views Asked by At

let A and B be sets with a maximum.

I want to know if:

$$ A \cap B $$

also has a maximum then.

I know that $$A \cap B $$

has a supremum and I already proofed that $$ sup(A \cap B) \le min\{supA,supB\} $$

Can someone help me? ;)

1

There are 1 best solutions below

1
On

You can take $A= (0,1) \cup (3,4]$ and $B= (0,2]$ as an counterexample. A has the maximum 4 and B has the maximum 2. The intersection is $A\cap B= (0,1)$ which doesn't attain its maximum.