Cartoon illustrating a three-point correlation (0 – 1 – 2) with different scales s₁ on the side (0 – 1) and s₂ on the side (0 – 2). Integration over spherical shells K₁ and K₂ is equivalent to counting all possible triangles that have one vertex at point 0 and the other two anywhere on the spheres. For the calculation of , the kernels are uniformly populated, while for the evaluation of the Legendre expansion coefficients they are populated with the values of . The values of m_i are scanned from −l_i to +l_i, resulting in 2(2l + 1) convolutions for each value of l, since both real and imaginary parts of Y_lm must be used.