Lithium be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than
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