Ley Koo, E., A. Góngora T., and H. Torres Bustamante. “Addendum to Complete Electromagnetic Multipole Expansion Including Toroidal Moments Rev. Mex. Fis E 52 (2006) 188-197”. Revista Mexicana De Física E, vol. 17, no. 2 Jul-Dec, July 2020, pp. 138-40, doi:10.31349/RevMexFisE.17.138.