<https://github.com/Libsharp/libsharp>.

<https://gitlab.mpcdf.mpg.de/mtr/libsharp> (previously
<https://github.com/Libsharp/libsharp>).

See also <https://arxiv.org/abs/1010.2084> for sYlm definitions and
conventions.

For sYlm definitions and conventions: see
<https://arxiv.org/abs/1010.2084>
For storage conventions for real functions: see appendix of de
Oliveira-Costa, A., Tegmark, M., Zaldarriaga, M., & Hamilton, A. 2004,
Phys. Rev. D, 69, 063516, arXiv:astro-ph/0307282