What is this symbol?

[misterau]

1. The problem statement, all variables and given/known data
http://img40.imageshack.us/img40/6421/57065635.jpg
3. The attempt at a solution
I just what to know what the hollow I symbol is?
Is it just
1 0 0
0 1 0
0 0 1
Thank you!

[Count Iblis]

Yes, it is the identity matrix.