External mathematical library functions such as those documented in
External Libraries that are invoked from virtual code by the
library combinator (Library combinator) are also
accessible from C by way of a uniform API implemented by the functions
declared in libfuns.h. This interface applies even to libraries
implemented in Fortran such as minpack. This section briefly
documents the functions in libfuns.h and sets out some
recommeded guidelines for developers wishing to add support for other
external libraries.