Yl1,m1⁡(θ,ϕ)⁢Yl2,m2⁡(θ,ϕ)=∑l,m((2⁢l1+1)⁢(2⁢l2+1)⁢(2⁢l+1)4⁢π)12⁢(l1l2lm1m2m)⁢Yl,m*⁡(θ,ϕ)⁢(l1l2l000),