A number of conversion functions, namely r_rint_, rint1,
irint, irintf, and irint1, are only available as part of the SUN sunmath library and need to be declared as extern C.
The relations id, char, bool, num,
irint, list and leaf are used to specify that the tree [a.sub.1] is an identifier, a character, a Boolean value, a real number, an integer or irrational number, a list, a label not of the form [<>.sup.a].