\[\int_{-1}^{1}\mathsf{P}^{m}_{l}\left(x\right)\mathsf{Q}^{m}_{n}\left(x\right)%
\,\mathrm{d}x=\frac{\left(1-(-1)^{l+n}\right)(l+m)!}{(l-n)(l+n+1)(l-m)!},\]