Editing Relational operator (section)

===Usage===
Equality is used in many programming language constructs and data types. It is used to test if an element already exists in a [[set (computer science)|set]], or to access to a value through a key. It is used in [[switch statement]]s to dispatch the control flow to the correct branch, and during the unification process in logic programming.

There can be multiple valid definitions of equality, and any particular language might adopt one or more of them, depending on various design aspects. One possible meaning of equality is that "if ''a'' equals ''b'', then either ''a'' or ''b'' can be used interchangeably in any context without noticing any difference". But this statement does not necessarily hold, particularly when taking into account mutability together with content equality.