Show that the spherical harmonics Yl,m are eigenfunctions of the parity operator with eigenvalue (−1)l. Note: An inversion of coordinates in spherical coordinates is accomplished by r→r, θ→π−θ, and ϕ→ϕ+π. Use (9.148). It may be wise to check the specific examples in (9.151) through (9.153) before attempting the general case.