UndirectedEdge[u, v] or u \[UndirectedEdge] v represents an undirected edge of a graph with vertices u and v.

Nest[f, expr, n] gives an expression with f applied n times to expr.

The Mathematica graphics language has many controls for preparing and laying out plots. Aligning plots is important when preparing graphics for presentation or publication.

DirectedEdge[u, v] or u \[DirectedEdge] v represents a directed edge from u to v.

MatrixExp[m] gives the matrix exponential of m. MatrixExp[m, v] gives the matrix exponential of m applied to the vector v.

WignerD[{j, m_1, m_2}, \[Psi], \[Theta], \[Phi]] gives the Wigner D-function D_m_1^m_2, j(\[Psi], \[Theta], \[Phi]).WignerD[{j, m_1, m_2}, \[Theta], \[Phi]] gives the Wigner ...

Simplifying expressions. Mathematica does not automatically simplify an algebraic expression like this. Simplify performs the simplification.

PolynomialQuotient[p, q, x] gives the quotient of p and q, treated as polynomials in x, with any remainder dropped.

PlotStyle is an option for plotting and related functions that specifies styles in which objects are to be drawn.

VectorAngle[u, v] gives the angle between the vectors u and v.