I have read that for a system of 2 particles, the total parity is given by:
$P=P_1 P_2 (-1)^L$ where
$ P_1, P_2$= insisec parity of particle 1, 2
$L$ = relative angular moment
what's the meaning of "relative angular moment"? Do I have to add the $l$ numbers of the two particles?
And what if I have 3 particles?