Triangle Condition

The condition that $j$ takes on the values

$$j=j_1+j_2, j_1+j_2-1, \ldots, \vert j_1-j_2\vert,$$

denoted $\Delta(j_1j_2j)$.

References

Sobelman, I. I. Atomic Spectra and Radiative Transitions, 2nd ed. Berlin: Springer-Verlag, p. 60, 1992.