Nuclear physics Pions and Parity?

Davorak

Why can:
[tex]
\pi^- + d \rightarrow n + n + \pi^0
[/tex]
not happen for pions at rest?

work so far:
[tex]
\begin{array}
{|c|c|c|c|c|c|}\hline&\pi^-&d&\rightarrow &n \ + \ n&\pi^0\\\hline{Spin}&0&1&\
\rightarrow &1/2 \ 1/2&0\\\hline{J}&0&1&\rightarrow &L + \
S&0\\\hline{Parity}&-1&1&\rightarrow &(-1)^{S+L+1}&-1\\\hline
\end{array}
[/tex]
d is deuterium
S+L for the nuetron pair must be even since they are identical fermions
Partity egeinvalues -1 != 1
I think the Paritiy inequality is the key, but i can not make the connection with a physical law.
Any help would be nice, Thanks

Edit: never mind I figuared it out. Aditional angular momentum on the left hand side will flip parity(l=1,3,5...), making parity conserved again. Thanks anyway