BondarenkoV. V., BondarenkoV. M., and PeregudaYu. N. 2012. “Local Deformations of Positive-Definite Quadratic Forms”. Ukrains’kyi Matematychnyi Zhurnal 64 (7), 892-907. https://umj.imath.kiev.ua/index.php/umj/article/view/2626.