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Infix notation is the notation commonly used inarithmetical andlogical formulae and statements. It is characterized by the placement ofoperators betweenoperands—"infixed operators"—such as theplus sign in2+ 2.
Binary relations are often denoted by an infix symbol such asset membershipa ∈A when the setA hasa for an element. Ingeometry,perpendicular linesa andb are denoted and inprojective geometry two pointsb andc are inperspective when while they are connected by a projectivity when
Infix notation is more difficult toparse by computers thanprefix notation (e.g.+ 2 2) orpostfix notation (e.g. 2 2+). However manyprogramming languages use it due to its familiarity. It is more used in arithmetic, e.g. 5× 6.[1]
Infix notation may also be distinguished fromfunction notation, where the name of a function suggests a particular operation, and itsarguments are the operands. An example of such afunction notation would beS(1, 3) in which the functionS denotes addition ("sum"):S (1, 3) = 1 + 3 = 4.
In infix notation, unlike in prefix or postfix notations,parentheses surrounding groups of operands and operators are necessary to indicate the intended order in which operations are to be performed. In the absence of parentheses, certain precedence rules determine theorder of operations.