 9-j symbol

In physics, Wigner's 9-"j" symbols were introduced by Eugene Paul Wigner in 1937.They are related to recoupling coefficients in quantum mechanics involving four angular momenta

Coupling of two angular momenta formula_2 and formula_3 is the construction of simultaneous eigenfunctions of formula_4 and formula_5, where formula_6, as explained in the article on Clebsch–Gordan coefficients.