The triangular delta { j 1 j 2 j 3 } is equal to 1 when the triad (j 1, j 2, j 3) satisfies the triangle conditions, and is zero otherwise. The triangular delta itself is sometimes confusingly called a "3- j symbol" (without the m) in analogy to 6- j and 9- j symbols, all of which are irreducible summations of 3- jm symbols where no m variables remain.