# Left and right Identities

1. Jan 16, 2012

### Punkyc7

If an operation has two left identities, show that it has no right identity.
$_{}$
pf/
Let e$_{1}$ and e$_{2}$ be left identities such that e$_{1}$≠e$_{2}$. Assume there exist a right identity and call it r.

Then we have that
e$_{1}$x=x
e$_{2}$x=x and
xr=x.

From here I want to try and show that there can not be a right identity but I don't see where to go.

2. Jan 16, 2012

### gb7nash

This is fine so far.

Try evaluating e1r. What two pieces of information can you conclude? Similarly...

3. Jan 16, 2012

### Punkyc7

wouldnt I get
e$_{1}$r=e$_{1}$=r

and

e$_{2}$r=e$_{2}$=r

So we get e$_{2}$ and e$_{1}$ are equal contradicting that they were distinct.

Is that right?

4. Jan 16, 2012

### gb7nash

Correct.

5. Jan 16, 2012

### Punkyc7

thanks, I was trying to figure it out with the x's and I couldnt come to any contradiction