 Racah coefficients have more convenient symmetry properties than the recoupling coefficients (but less convenient than the 6-"j" symbols).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.The result is 
where formula_8 and formula_9.