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  2. List of set identities and relations - Wikipedia

    en.wikipedia.org/wiki/List_of_set_identities_and...

    A universe set is an absorbing element of binary union . The empty set ∅ {\displaystyle \varnothing } is an absorbing element of binary intersection ∩ {\displaystyle \cap } and binary Cartesian product × , {\displaystyle \times ,} and it is also a left absorbing element of set subtraction ∖ : {\displaystyle \,\setminus :}

  3. Preorder - Wikipedia

    en.wikipedia.org/wiki/Preorder

    The relation on equivalence classes is a partial order. In mathematics, especially in order theory, a preorder or quasiorder is a binary relation that is reflexive and transitive. The name preorder is meant to suggest that preorders are almost partial orders, but not quite, as they are not necessarily antisymmetric.

  4. Direct product of groups - Wikipedia

    en.wikipedia.org/wiki/Direct_product_of_groups

    The binary operation on G × H is associative. Identity The direct product has an identity element, namely (1 G, 1 H), where 1 G is the identity element of G and 1 H is the identity element of H. Inverses The inverse of an element (g, h) of G × H is the pair (g −1, h −1), where g −1 is the inverse of g in G, and h −1 is the inverse of ...

  5. Monoid - Wikipedia

    en.wikipedia.org/wiki/Monoid

    One does this by specifying a set of generators Σ, and a set of relations on the free monoid Σ ∗. One does this by extending (finite) binary relations on Σ ∗ to monoid congruences, and then constructing the quotient monoid, as above. Given a binary relation R ⊂ Σ ∗ × Σ ∗, one defines its symmetric closure as R ∪ R −1.

  6. Directed set - Wikipedia

    en.wikipedia.org/wiki/Directed_set

    Here the order relation on the elements of is inherited from ; for this reason, reflexivity and transitivity need not be required explicitly. A directed subset of a poset is not required to be downward closed; a subset of a poset is directed if and only if its downward closure is an ideal. While the definition of a directed set is for an ...

  7. Division by zero - Wikipedia

    en.wikipedia.org/wiki/Division_by_zero

    It is in the formal proof that this relation is an equivalence relation that the requirement that the second coordinate is not zero is needed (for verifying transitivity). [ 24 ] [ 25 ] [ 26 ] Although division by zero cannot be sensibly defined with real numbers and integers, it is possible to consistently define it, or similar operations, in ...

  8. Recurrence relation - Wikipedia

    en.wikipedia.org/wiki/Recurrence_relation

    In mathematics, a recurrence relation is an equation according to which the th term of a sequence of numbers is equal to some combination of the previous terms. Often, only previous terms of the sequence appear in the equation, for a parameter that is independent of ; this number is called the order of the relation.

  9. Dirichlet convolution - Wikipedia

    en.wikipedia.org/wiki/Dirichlet_convolution

    The multiplicative identity is the unit function ε defined by ε(n) = 1 if n = 1 and ε(n) = 0 if n > 1. The units (invertible elements) of this ring are the arithmetic functions f with f(1) ≠ 0. Specifically, [1] Dirichlet convolution is associative, = (), distributive over addition