A dialect of Lisp developed in 1967 by Bolt, Beranek and Newman (Cambridge, MA) as a descendant of BBN-Lisp. It emphasises user interfaces. It is currently supported by Xerox PARC. Interlisp was one of two main branches of LISP (the other being MACLISP). In 1981 Common LISP was begun in an effort to combine the best features of both. Interlisp includes a Lisp programming environment. It is dynamically scoped. LAMBDA functions evaluate their arguments, NLAMBDA functions do not. Any function could be called with optional arguments. See also AM, CLISP, Interlisp-10, Interlisp-D.