Taking the upper sign with the condition that M = J gives initial recursion relation: 0 = C + ( j 1 , m 1 − − 1 ) ⟨ ⟨ j 1 ( m 1 − − 1 ) j 2 m 2 | J J ⟩ ⟩ + C + ( j 2 , m 2 − − 1 ) ⟨ ⟨ j 1 m 1 j 2 ( m 2 − − 1 ) | J J ⟩ ⟩ . In the Condon–Shortley phase convention, one adds the constraint that