Acronym for Reverse Polish Notation.
The idea of putting your operators after your arguments. Arguments are "pushed" onto a stack, and an operator pop's off the required arguments, computes the result and pushes it back onto the stack. For example:
3 1 2 + *
leaves 6 on the stack. Note that RPN doesn't require any brackets.
Compare InfixNotation?, PrefixNotation
2 pages link to RPN:
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