Styles of syntax used for writing expressions or tree-structured data:
Infix notation is the usual. It needs precedence rules and/or brackets to make the order of operations unambiguous. Polish and Reverse Polish don't have that problem, providing the number arguments to each operator is fixed.
In Reverse Polish, or postfix, notation you write the operator after the arguments.
In Polish, or prefix, notation you write the operator before the arguments.
Polish notation is called that because a famous Polish mathematician first used it for Boolean algebra, and nobody can either remember or pronounce his name without looking it up first. (You go look it up.)
It's very easy to parse this notation into tree structures, which is why LISP uses it.
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