In computer science, a relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities. These include numerical equality (e.g., ) and inequalities (e.g., ). In programming languages that include a distinct boolean data type in their type system, like Pascal, Ada, or Java, these operators usually evaluate to true or false, depending on if the conditional relationship between the two operands holds or not. In languages such as C, relational operators return the integers 0 or 1, where 0 stands for false and any non-zero value stands for true. An expression created using a relational operator forms what is termed a relational expression or a condition. Relational operators can be seen as special cases of logical predicates. Equality 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, or to access to a value through a key. It is used in switch statements to dispatch the control flow to the correct branch, and during the unification process in logic programming. 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. Location equality vs. content equality Sometimes, particularly in object-oriented programming, the comparison raises questions of data types and inheritance, equality, and identity. It is often necessary to distinguish between: two different objects of the same type, e.g., two hands two objects being equal but distinct, e.g., two $10 banknotes two objects being equal but having different representation, e.g., a $1 bill and a $1 coin two different references to the same object, e.g., two nicknames for the same person In many modern programming languages, objects and data structures are accessed through references. In such languages, there becomes a need to test for two different types of equality: Location equality (identity): if two references (A and B) reference the same object. Interactions with the object through A are indistinguishable from the same interactions through B, and in particular changes to the object through A are reflected through B. Content equality: if the objects referenced by two references (A and B) are equivalent in some sense: Structural equality (that is, their contents are