In Common Lisp, T is the "any" type (which makes sense there, as type specifiers can be formed using unions using (or type-A type-B ...) lists), the value NIL i

In Common Lisp, T is the "any" type (which makes sense there, as type specifiers can be formed using unions using (or type-A type-B ...) lists), the value NIL is the sole instance of the type NULL.