to be called using prefix notation, while still supporting the unary postfix syntax common in other languages. The number of return values of an expression equals the difference between the number of operands in an expression and the total arity of the operators minus the total number of return values of the operators. Polish notation, usually in postfix form, is the chosen notation of certain calculators, notably from Hewlett-Packard. At a lower level, postfix operators are used by some stack machines such as the Burroughs large systems. See also Reverse Polish notation (RPN) Function application Lambda calculus Currying Lisp (programming language) S-expression Polish School of Mathematics Hungarian notation Verb–subject–object (VSO) Verb–object–subject (VOS) Head-directionality parameter WFF 'N PROOF References Further reading Translated by H. Weber in Storrs McCall, Polish Logic 1920–1939, Clarendon Press: Oxford (1967). (77 pages) (11 pages) (NB. Published in .) (11 pages) External links Mathematical notation Polish inventions Science and technology in Poland Operators (programming) Logical expressions