Nuprl is implemented in Lisp as a function; therefore, entering the Nuprl environment entails first invoking Lisp. Currently there are two implementations, one running on a Symbolics Lisp Machine and one written in Franz Lisp and running on Unix. One invokes the Nuprl environment using commands which load the system in the appropriate Lisp environment. The system comes up with a two--window display as in figure .
Figure: The Initial Display
P> is the top--level prompt from the command module. Depending on its mode, the window may display one of several prompts The modes and their corresponding prompts are: