https://docs.oracle.com/cd/E88353_01/html/E37846/y0f-3m.html
y0f - man pages section 3: Extended Library Functions, Volume 2
y0 , y0f , y0l , y1 , y1f , y1l , yn , ynf , ynl - Bessel functions of the second kind
man pagesextended librarysectionfunctionsvolume