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A function [d] A relation that is functional and total. For example, the red and green relations in the diagram are functions, but the blue and black ones are not. An injection [d] A function that is injective. For example, the green relation in the diagram is an injection, but the red, blue and black ones are not. A surjection [d]
Thomae's function: is a function that is continuous at all irrational numbers and discontinuous at all rational numbers. It is also a modification of Dirichlet function and sometimes called Riemann function. Kronecker delta function: is a function of two variables, usually integers, which is 1 if they are equal, and 0 otherwise.
This article lists mathematical properties and laws of sets, involving the set-theoretic operations of union, intersection, and complementation and the relations of set equality and set inclusion. It also provides systematic procedures for evaluating expressions, and performing calculations, involving these operations and relations.
Mathematical relations fall into various types according to their specific properties, often as expressed in the axioms or definitions that they satisfy. Many of these types of relations are listed below.
These relations can be justified by an argument analogous to the one by comparing coefficients in power series given above, based in this case on the generating function identity ∑ k = 0 ∞ h k ( x 1 , … , x n ) t k = ∏ i = 1 n 1 1 − x i t . {\displaystyle \sum _{k=0}^{\infty }h_{k}(x_{1},\ldots ,x_{n})t^{k}=\prod _{i=1}^{n}{\frac {1 ...
The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.
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In the case where R is a binary relation, those statements are also denoted using infix notation by x 1 Rx 2. The following considerations apply: The set X i is called the i th domain of R. [1] In the case where R is a binary relation, X 1 is also called simply the domain or set of departure of R, and X 2 is also called the codomain or set of ...