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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. Directed set - Wikipedia

    en.wikipedia.org/wiki/Directed_set

    In mathematics, a directed set (or a directed preorder or a filtered set) is a nonempty set together with a reflexive and transitive binary relation (that is, a preorder), with the additional property that every pair of elements has an upper bound. [1]

  4. Direct product of groups - Wikipedia

    en.wikipedia.org/wiki/Direct_product_of_groups

    The resulting algebraic object satisfies the axioms for a group. Specifically: Associativity 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.

  5. Total order - Wikipedia

    en.wikipedia.org/wiki/Total_order

    A binary relation that is antisymmetric, transitive, and reflexive (but not necessarily total) is a partial order. A group with a compatible total order is a totally ordered group. There are only a few nontrivial structures that are (interdefinable as) reducts of a total order. Forgetting the orientation results in a betweenness relation.

  6. Preorder - Wikipedia

    en.wikipedia.org/wiki/Preorder

    Every binary relation on a set can be extended to a preorder on by taking the transitive closure and reflexive closure, + =. The transitive closure indicates path connection in R : x R + y {\displaystyle R:xR^{+}y} if and only if there is an R {\displaystyle R} - path from x {\displaystyle x} to y . {\displaystyle y.}

  7. Crystal structure - Wikipedia

    en.wikipedia.org/wiki/Crystal_structure

    Crystal structure is described in terms of the geometry of arrangement of particles in the unit cells. The unit cell is defined as the smallest repeating unit having the full symmetry of the crystal structure. [2]

  8. Cartesian product - Wikipedia

    en.wikipedia.org/wiki/Cartesian_product

    Cartesian product of the sets {x,y,z} and {1,2,3}In mathematics, specifically set theory, the Cartesian product of two sets A and B, denoted A × B, is the set of all ordered pairs (a, b) where a is in A and b is in B. [1]

  9. Wikipedia:Reference desk/Archives/Science/December 2005 ...

    en.wikipedia.org/wiki/Wikipedia:Reference_desk/...

    How can one convert a .m4a file format (songs from iTunes) to *.wma file format (so i can play them in windows media player...)? There's a winamp plugin that lets it play m4a. So you can use winamp to play them, or you can use winamp to decode it to a wav (and then you can use any of a dozen programs to reencode it as an mp3) Raul654 10:58, 1 ...