Kurt Bernardo Wolf. “Transformation Matrices Between the U$_3 \supset$ U$_2$ and U$_3 \supset $ O$_3$ Chains”. Revista Mexicana De Física, vol. 19, no. 2, Jan. 1970, pp. 206-25, https://rmf.smf.mx/ojs/index.php/rmf/article/view/959.