Function-names
A function-name specifies the mechanism provided to determine the value of an intrinsic function or a user-defined function.
The same word,
in a different context, can appear in a program as a user-defined word or a system name. For a list
of intrinsic function names and their definitions, see Table 1.
Intrinsic function names may be used as user-defined function-names, except for LENGTH, RANDOM, SIGN, SUM, and WHEN-COMPILED.