# Looking the name

• Mar 30th 2011, 04:24 PM
Connected
Looking the name
If $\displaystyle x\in A$ verifies that $\displaystyle \forall\epsilon:B(x,\epsilon)\cap A\ne\varnothing,$ how is it called?

Thank you!
• Mar 30th 2011, 04:48 PM
bkarpuz
Quote:

Originally Posted by Connected
If $\displaystyle x\in A$ verifies that $\displaystyle \forall\epsilon:B(x,\epsilon)\cap A\ne\varnothing,$ how is it called?

Is there a typo here?
Because this is always true since $\displaystyle x\in B(x,\epsilon)\cap A$.
• Mar 30th 2011, 04:54 PM
Connected
No, no typo, it's just that I want to know how the point $\displaystyle x$ is called.
• Mar 30th 2011, 04:58 PM
bkarpuz
Quote:

Originally Posted by Connected
No, no typo, it's just that I want to know how the point $\displaystyle x$ is called.

Then I want to learn this too. :)
• Mar 30th 2011, 05:02 PM
Connected
Haha, okay, perhaps another known example:

$\displaystyle x\in A$ is said to be an interior point of $\displaystyle A$ if $\displaystyle \exists\delta>0:B(x,\delta)\subseteq A.$
• Mar 30th 2011, 05:08 PM
bkarpuz
$\displaystyle x\in X$ is said to be an accumulation (limit) point of $\displaystyle A$
provided that $\displaystyle (B(x,\varepsilon)\backslash\{x\})\cap A\neq\emptyset$ for every $\displaystyle \varepsilon>0$.

May be you are looking for this one?
• Mar 30th 2011, 05:13 PM
Connected
Got it, the concept is "adherent point."
• Mar 30th 2011, 05:14 PM
Drexel28
Quote:

Originally Posted by Connected
Got it, the concept is "adherent point."

What you mean to say is that $\displaystyle x\in A$ or etc.
• Mar 30th 2011, 05:18 PM
Connected
I think the other name that has is "closure point," does that make sense?