This document describes a Lisp interpreter implemented in Postscript. It summarizes key concepts used including: 1) Using dictionaries to parse code and change parsing state. Different dictionaries are used for different contexts like procedure definition vs normal code. 2) The eval function reorders operands on the stack before applying functions. 3) Dictionaries are used to map Scheme special forms and variables to Postscript words. 4) Lists are represented by arrays and functions like cons, car, cdr are defined to manipulate them. 5) Lambda functions are implemented via code injection - generating Postscript code for the function body and enclosing it.