Of females that give birth, 90% have twins, but singletons and triplets are also possible. There have been reported cases of twin births, but singletons are vastly more common. Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. Single vertices are not considered clusters and are grouped into a singletons set S. The atoms here are the singletons, those subsets with exactly one element. Prokaryotic cells are usually singletons, while eukaryotic cells are usually found in multicellular organisms. At the initial step, all clusters are singletons (clusters containing a single point). However, this includes the (one) empty set, and "N" singletons, which are not properly subgroups. But the only nonempty sets of diameter 0 are singletons. Hausdorff spaces are T, meaning that all singletons are closed. In addition, many believe that worthless singletons and doubletons are generally overvalued. These four Singletons are referred to as the Core Actors. IANA is responsible for allocating singletons. Geminates are 1.5 to 2 times longer than singletons, depending, primarily, on position and stress. It is also T, as all singletons are closed.