3. Empty listorFalse. In Lisp, the empty list (or "nil list") is used to represent the Booleanvalue False. This is possible because Lisp is not typed. True is represented by the special atom "t".
4. Spoken in reply to a question, particularly one asked using the "-P" convention it means "No". Most hackers assume this derives simply from LISP, but NIL meaning "no" was well-established among radio hams decades before LISP existed. The historical connection between early hackerdom and the ham radio world was strong enough that this may have been an influence.