Reverse Polish Notation

Reverse Polish notation, or RPN, is an alternative to the familiar infix notation for mathematical expressions in which operations appear after their arguments rather than before or between them.
For example, the infix expression
\[ x - y \]
is written in RPN as
\[ x \; y \; - \]
One of the advantages of RPN is that it can unambiguously represent expressions without the need for brackets.
For example
\[ (x + 1) \times (y - 1) \]
can be written as
\[ x \; 1 \;+ \; y \; 1 \; - \times \]