# Angular momentum in bracket notation

1. Sep 27, 2011

### Alexis21

Hello,

why is

$<j' m' | j m>=0$

if

$j \not= j' \; \text{or} \; m \not= m'$

j and m are describing states. I don't understand why an 'empty bracket' behaves like that.

2. Sep 27, 2011