5 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/acosf.html}
9 Portability problems fixed by Gnulib:
13 Portability problems not fixed by Gnulib:
16 This function is missing on some platforms:
17 Minix 3.1.8, AIX 5.1, Solaris 9.