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  2. List of space groups - Wikipedia

    en.wikipedia.org/wiki/List_of_space_groups

    In Hermann–Mauguin notation, space groups are named by a symbol combining the point group identifier with the uppercase letters describing the lattice type. Translations within the lattice in the form of screw axes and glide planes are also noted, giving a complete crystallographic space group. These are the Bravais lattices in three dimensions:

  3. Group structure and the axiom of choice - Wikipedia

    en.wikipedia.org/wiki/Group_Structure_and_the...

    If a set is such that it cannot be endowed with a group structure, then it is necessarily non-wellorderable. Otherwise the construction in the second section does yield a group structure. However these properties are not equivalent. Namely, it is possible for sets which cannot be well-ordered to have a group structure.

  4. Point groups in four dimensions - Wikipedia

    en.wikipedia.org/wiki/Point_groups_in_four...

    Download as PDF; Printable version ... disorganised with no clear sense of structure. ... order.index) by their abstract group structure. [15] Finite groups ...

  5. Group theory - Wikipedia

    en.wikipedia.org/wiki/Group_theory

    In abstract algebra, group theory studies the algebraic structures known as groups. The concept of a group is central to abstract algebra: other well-known algebraic structures, such as rings, fields, and vector spaces, can all be seen as groups endowed with additional operations and axioms. Groups recur throughout mathematics, and the methods ...

  6. Preadditive category - Wikipedia

    en.wikipedia.org/wiki/Preadditive_category

    There is a convenient relationship between the kernel and cokernel and the abelian group structure on the hom-sets. Given parallel morphisms f and g, the equaliser of f and g is just the kernel of g − f, if either exists, and the analogous fact is true for coequalisers. The alternative term "difference kernel" for binary equalisers derives ...

  7. Quotient group - Wikipedia

    en.wikipedia.org/wiki/Quotient_group

    The quotient group is the same idea, although one ends up with a group for a final answer instead of a number because groups have more structure than an arbitrary collection of objects: in the quotient ⁠ / ⁠, the group structure is used to form a natural "regrouping".

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  9. Strukturbericht designation - Wikipedia

    en.wikipedia.org/wiki/Strukturbericht_designation

    In crystallography, a Strukturbericht designation or Strukturbericht type is a system of detailed crystal structure classification by analogy to another known structure. The designations were intended to be comprehensive but are mainly used as supplement to space group crystal structures designations, especially historically.