\begin{definition}[Definition:Polish Notation]
'''Polish notation''' is a method of writing expressions without the need for parentheses.
The main method in writing an expression in '''Polish notation''' is to output an operator $\Box$, directly followed by the output of all its arguments $p, q, \ldots$, yielding:
:$\Box p q \ldots$
If we had another, operator $\diamond$ taking only one argument, then also:
:$\Box {\diamond} p {\diamond} q \ldots$
is in '''Polish notation'''.
Note that for the applicability of '''Polish notation''', it is vital to be able to efficiently distinguish an argument from an operator, or a sequence of arguments.
\end{definition}