SystemOpen["target"] opens the specified file, URL, or other target with the associated program on your computer system.

SystemsModelLabels is an option to StateSpaceModel and TransferFunctionModel that specifies labels of the variables.

TraceForward is an option for Trace and related functions which specifies whether to include later expressions on the evaluation chain that contains the pattern form sought.

Uncompress["string"] recovers an expression from a compressed string representation generated by Compress.Uncompress["string", h] wraps the head h around the expression ...

Undefined is a symbol that represents a quantity with no defined value.

Underoverscript[x, y, z] is an object that formats as x_y^z.

lhs =!= rhs yields True if the expression lhs is not identical to rhs, and yields False otherwise.

UnsetShared[s_1, s_2, ...] stops the sharing of the variables or functions s_i among parallel kernels.UnsetShared[patt] stops the sharing of all variables and functions whose ...

VertexAdd[g, v] makes a graph by adding the vertex v to the graph g.VertexAdd[g, {v_1, v_2, ...}] adds a collection of vertices to g.

VertexDelete[g, v] makes a graph by deleting the vertex \[Nu] and all edges connected to v from the graph g.VertexDelete[g, {v_1, v_2, ...}] deletes a collection of vertices ...