SimpleGraph[g] gives the underlying simple graph from the graph g.
SpheroidalPSPrime[n, m, \[Gamma], z] gives the derivative with respect to z of the angular spheroidal function PS n, m (\[Gamma], z) of the first kind.
SpheroidalQSPrime[n, m, \[Gamma], z] gives the derivative with respect to z of the angular spheroidal function QS n, m (\[Gamma], z) of the second kind.
StringCount["string", " sub"] gives a count of the number of times " sub" appears as a substring of " string". StringCount["string", patt] gives the number of substrings in " ...
Subgraph[g, {v_1, v_2, ...}] gives the subgraph of the graph g generated by the vertices v_i.Subgraph[g, {e_1, e_2, ...}] gives the subgraph generated by the edges ...
SyntaxInformation[f] gives information used to generate syntax coloring and other advisories when f[...] is entered as input.
Tan
(Built-in Mathematica Symbol) Tan[z] gives the tangent of z.
UndirectedGraphQ[g] yields True if the graph g is an undirected graph and False otherwise.
UniformGraphDistribution[n, m] represents a uniform graph distribution on n-vertex, m-edge graphs.
UnitBox
(Built-in Mathematica Symbol) UnitBox[x] represents the unit box function, equal to 1 for |x| <= 1/2 and 0 otherwise.UnitBox[x_1, x_2, ...] represents the multidimensional unit box function, equal to 1 if ...