 Apart from a phase factor, Racah's W-coefficients are equal to Wigner's 6-j symbols, so any equation involving Racah's W-coefficients may be rewritten using 6-"j" symbols.This is often advantageous because the symmetry properties of 6-"j" symbols are easier to remember.Racah coefficients are related to recoupling coefficients by
Recoupling coefficients are elements of a unitary transformation and their definition is given in the next section.