Abundance of the chemical elements in the Sun and outer planets is similar to that in the universe. Due to solar heating, the elements of Earth and the inner rocky planets of the Solar System have undergone an additional depletion of volatile hydrogen, helium, neon, nitrogen, and carbon (which volatilizes as methane). The crust, mantle, and core of the Earth show evidence of chemical segregation plus some sequestration by density. Lighter silicates of aluminum are found in the crust, with more magnesium silicate in the mantle, while metallic iron and nickel compose the core. The abundance of elements in specialized environments, such as atmospheres, or
Semigroup with two elements Semigroup with two elements In mathematics, a semigroup with two elements is a semigroup for which the cardinality of the underlying set is two. There are exactly five distinct nonisomorphic semigroups having two elements: The semigroups LO and RO are antiisomorphic. O, and are commutative, LO and RO are noncommutative. LO, RO and are bands and also inverse semigroups. Choosing the set "A" = { 1, 2 } as the underlying set having two elements, sixteen binary operations can be defined in "A". These operations are shown in the table below. In the table, a matrix of the form indicates