 CL follows the older Lisp convention of using the symbols T and NIL, with NIL standing also for the empty list.In CL, "any" non-NIL value is treated as true by conditionals, such as codice_68, whereas in Scheme all non-#f values are treated as true.These conventions allow some operators in both languages to serve both as predicates (answering a boolean-valued question) and as returning a useful value for further computation, but in Scheme the value '() which is equivalent to NIL in Common Lisp evaluates to true in a boolean expression.