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  2. Dihedral group of order 6 - Wikipedia

    en.wikipedia.org/wiki/Dihedral_group_of_order_6

    In fact the two cyclic permutations of all three blocks, with the identity, form a subgroup of order 3, index 2, and the swaps of two blocks, each with the identity, form three subgroups of order 2, index 3. The existence of subgroups of order 2 and 3 is also a consequence of Cauchy's theorem. The first-mentioned is { (), (RGB), (RBG) }, the ...

  3. List of character tables for chemically important 3D point groups

    en.wikipedia.org/wiki/List_of_character_tables...

    For each non-linear group, the tables give the most standard notation of the finite group isomorphic to the point group, followed by the order of the group (number of invariant symmetry operations). The finite group notation used is: Z n : cyclic group of order n , D n : dihedral group isomorphic to the symmetry group of an n –sided regular ...

  4. Alchemical symbol - Wikipedia

    en.wikipedia.org/wiki/Alchemical_symbol

    Alchemical symbols were used to denote chemical elements and compounds, as well as alchemical apparatus and processes, until the 18th century. Although notation was ...

  5. Water pollution - Wikipedia

    en.wikipedia.org/wiki/Water_pollution

    A practical definition of water pollution is: "Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses." [1]: 6 Water is typically referred to as polluted when it is impaired by anthropogenic contaminants.

  6. List of spherical symmetry groups - Wikipedia

    en.wikipedia.org/wiki/List_of_spherical_symmetry...

    The group order is defined as the subscript, unless the order is doubled for symbols with a plus or minus, "±", prefix, which implies a central inversion. [ 3 ] Hermann–Mauguin notation (International notation) is also given.

  7. United States regulation of point source water pollution

    en.wikipedia.org/wiki/United_States_regulation...

    Water pollution is the contamination of natural water bodies by chemical, physical, radioactive or pathogenic microbial substances. [2] Point sources of water pollution are described by the CWA as "any discernible, confined, and discrete conveyance from which pollutants are or may be discharged."

  8. GHS hazard pictograms - Wikipedia

    en.wikipedia.org/wiki/GHS_hazard_pictograms

    Division 1.3: Substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard Note : The asterisks are replaced by the class number and compatibility code

  9. Wastewater quality indicators - Wikipedia

    en.wikipedia.org/wiki/Wastewater_quality_indicators

    Nonpoint source pollution can be contrasted with point source pollution, where discharges occur to a body of water at a single location. The nonpoint sources of phosphates include natural decomposition of rocks and minerals, stormwater runoff , agricultural pollution , erosion and sedimentation , atmospheric deposition , and direct input by ...