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  2. Covering groups of the alternating and symmetric groups

    en.wikipedia.org/wiki/Covering_groups_of_the...

    For n = 4, the Schur cover of the alternating group is given by SL(2, 3) → PSL(2, 3) ≅ A 4, which can also be thought of as the binary tetrahedral group covering the tetrahedral group. Similarly, GL(2, 3) → PGL(2, 3) ≅ S 4 is a Schur cover, but there is a second non-isomorphic Schur cover of S 4 contained in GL(2,9) – note that 9 = 3 ...

  3. Alternating group - Wikipedia

    en.wikipedia.org/wiki/Alternating_group

    A 4 is isomorphic to PSL 2 (3) [1] and the symmetry group of chiral tetrahedral symmetry. A 5 is isomorphic to PSL 2 (4), PSL 2 (5), and the symmetry group of chiral icosahedral symmetry. (See [1] for an indirect isomorphism of PSL 2 (F 5) → A 5 using a classification of simple groups of order 60, and here for a direct proof). A 6 is ...

  4. Automorphisms of the symmetric and alternating groups

    en.wikipedia.org/wiki/Automorphisms_of_the...

    the product of two 2-cycles such as (1 2)(3 4) maps to another product of two 2-cycles such as (3 5)(4 6), accounting for 45 permutations; the product of a 2-cycle and a 4-cycle such as (1 2 3 4)(5 6) maps to another such permutation such as (1 4 2 6)(3 5), accounting for the 90 remaining permutations. And the odd part is also conserved:

  5. Parallel postulate - Wikipedia

    en.wikipedia.org/wiki/Parallel_postulate

    Euclid gave the definition of parallel lines in Book I, Definition 23 [2] just before the five postulates. [3] Euclidean geometry is the study of geometry that satisfies all of Euclid's axioms, including the parallel postulate. The postulate was long considered to be obvious or inevitable, but proofs were elusive.

  6. Tetradecagon - Wikipedia

    en.wikipedia.org/wiki/Tetradecagon

    The highest symmetry irregular tetradecagons are d14, an isogonal tetradecagon constructed by seven mirrors which can alternate long and short edges, and p14, an isotoxal tetradecagon, constructed with equal edge lengths, but vertices alternating two different internal angles.

  7. Transversal (geometry) - Wikipedia

    en.wikipedia.org/wiki/Transversal_(geometry)

    A transversal produces 8 angles, as shown in the graph at the above left: 4 with each of the two lines, namely α, β, γ and δ and then α 1, β 1, γ 1 and δ 1; and; 4 of which are interior (between the two lines), namely α, β, γ 1 and δ 1 and 4 of which are exterior, namely α 1, β 1, γ and δ.

  8. Bilinski dodecahedron - Wikipedia

    en.wikipedia.org/wiki/Bilinski_dodecahedron

    Because of its reversal, the Bilinski dodecahedron has a lower order of symmetry; its symmetry group is that of a rectangular cuboid: D 2h, [2,2], (*222), of order 8. This is a subgroup of octahedral symmetry; its elements are three 2-fold symmetry axes, three symmetry planes (which are also the axial planes of this solid), and a center of inversion symmetry.

  9. Complete graph - Wikipedia

    en.wikipedia.org/wiki/Complete_graph

    Complete bipartite graph (or biclique), a special bipartite graph where every vertex on one side of the bipartition is connected to every vertex on the other side The simplex , which is identical to a complete graph of n + 1 {\displaystyle n+1} vertices, where n {\displaystyle n} is the dimension of the simplex.