Place each operator before its operands. With known operator arities and unambiguous tokens, the abstract syntax tree is recovered recursively without precedence rules or parentheses. A binary application is encoded by its operator, the first subtree's encoding and the second subtree's encoding: this is a preorder traversal of the expression tree.
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Polish notation, also known as prefix notation, is a mathematical notation in which the operator precedes its operands. This means that instead of writing an expression in the conventional infix notation (where operators are placed between operands), Polish notation allows for expressions to be written without the need for parentheses to denote order of operations.