# Thread: Boolean Algebra

1. ## Boolean Algebra

In order to show a Lattice is a Boolean Algebra, the diagram needs to be bounded, distributive, complemented, and $|L|=2^n \ n\geq 1 \ n\in\mathbb{Z}$.

However, my book says, "A finite lattice is called a Boolean Algebra if it is isomorphic to $B_n$ for some nonnegative integer n."

What is $B_n$?

I know $D_n$ are the numbers that divide n but have no clue about this $B_n$.

Thanks.

2. Originally Posted by dwsmith
In order to show a Lattice is a Boolean Algebra, the diagram needs to be bounded, distributive, complemented, and $|L|=2^n \ n\geq 1 \ n\in\mathbb{Z}$.

However, my book says, "A finite lattice is called a Boolean Algebra if it is isomorphic to $B_n$ for some nonnegative integer n."

What is $B_n$?

I know $D_n$ are the numbers that divide n but have no clue about this $B_n$.

Thanks.
I'm not quite sure what they mean, but a fundamental result in the study of Boolean algebras is that every finite Boolean algebra $B$ is isomorphic to $2^{[n]}$ (here $[n]=\{1,\cdots,n\}$) for some $n\in\mathbb{N}$. This fact would make me guess that $B_n=2^{[n]}$.

3. So if $\displaystyle |L|=8$, what am I showing it is isomorphic too?

4. Originally Posted by dwsmith
So if $\displaystyle |L|=8$, what am I showing it is isomorphic too?
$2^{[3]}$.

5. Originally Posted by Drexel28
$2^{[3]}$.
Unfortunately, that didn't help. I understand $8=2^3$ but how do I show it is isomorphic to $2^3$?

6. Originally Posted by dwsmith
Unfortunately, that didn't help. I understand $8=2^3$ but how do I show is isomorphic to $2^3$?
This isn't in general easy. The result takes a fair amount of background. Do you know what 'atomic' means?

7. Haven't a clue unless you are talking about the science sense or as in bomb.

8. Originally Posted by dwsmith
Haven't a clue unless you are talking about the science sense or as in bomb.
Hahaha. Nice. Then what do you have?

9. The book mentions making a Hasse diagram of $B_n$. What would that look like?

Here is the Hasse diagram I need to show it is isomorphic to B_n.

Labeled a to h. a=O and h=I

10. Originally Posted by dwsmith
The book mentions making a Hasse diagram of $B_n$. What would that look like?

Here is the Hasse diagram I need to show it is isomorphic to B_n.

Labeled a to h. a=O and h=I

Here is the Hasse diagram for $2^{[3]}$

11. How is that the Hasse Diagram for $2^3\mbox{?}$ How do I come up with the Hasse diagram when I have $2^n$ is the better question?

12. Originally Posted by dwsmith
How is that the Hasse Diagram for $2^3\mbox{?}$ How do I come up with the Hasse diagram when I have $2^n$ is the better question?
Because it's the set of all subsets of a set with three elements. You do the same thing. Just draw out the diagram of the lattice for the power set of $\{1,2\}$.

13. So 4 is the P(s)={1,2,3,4} for instance?

14. Originally Posted by dwsmith
So 4 is the P(s)={1,2,3,4} for instance?
What I mean, is that if you have a Boolean algebra $B$ with $\#(B)=2^n$ then $B\cong\mathcal{P}\left(\{1,\cdots,n\}\right)$ if that notation is more comfortable.