GorbachukV. I. and GorbachukM. L. (1966) “On the representation of the vacuum mean of field operators in a space with an indefinite metrics”, Ukrains’kyi Matematychnyi Zhurnal, 18(6), pp. 108-111. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8464 (Accessed: 24November2024).