** Reverse Polish Notation**

Reverse Polish Notation (RPN) is an unambiguous, parenthesis-free notation for arithmetic expressions. [The description "Polish" refers to the nationality of logician Jan ukasiewicz, who invented (prefix) Polish notation in the 1920s. -- Wikipedia] Operands precede the operators that apply to them:

A + (B * C) --> A B C * + (A + B) * C --> A B + C *

It is easy to produce RPN as output of an operator precedence parser:

- Operands go directly to the output; no operand stack is used.
- When an operator is reduced, it is removed from the operator stack and put into the output.