Malyuta, Yu. M., and T. V. Obikhod. “BPS-States in F-Theory”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 54, no. 9, Sept. 2002, pp. 1284-8,
https://umj.imath.kiev.ua/index.php/umj/article/view/4167
.