Reverse Polish notation (
RPN) is a mathematical notation in which every
operator follows all of its
operands, in contrast to
Polish notation (PN), which puts the operator in the prefix position. It is also known as
postfix notation and is parenthesis-free as long as operator
arities are fixed. The description "Polish" refers to the
nationality of
logician Jan Lukasiewicz, who invented (prefix) Polish notation in the 1920s.