Lithium Lithium Lithium (from ) is a chemical element with symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element. Like all alkali metals, lithium is highly reactive and flammable, and is stored in mineral oil. When cut, it exhibits a metallic luster, but moist air corrodes it quickly to a dull silvery gray, then black tarnish. It never occurs freely in nature, but only in (usually ionic) compounds, such as pegmatitic minerals which were once the main source of lithium. Due to its solubility
E-dense semigroup introduced by Gabriel Thierrin in 1955. Some authors use "E"-dense to refer only to "E"-inversive semigroups in which the idempotents commute. More generally, a subsemigroup "T" of "S" is said dense in "S" if, for all "x" ∈ "S", there exists "y" ∈ "S" such that both "xy" ∈ "T" and "yx" ∈ "T". A semigroup with zero is said to be an "E"*-dense semigroup if every element other than the zero has at least one non-zero weak inverse. Semigroups in this class have also been called 0-inversive semigroups. E-dense semigroup In abstract algebra, an E"-dense semigroup (also called an