Nikolova, Stela. “$\prod_{1}^{0}$-POSITIVE INDUCTIVE DEFINABILITY ON ABSTRACT STRUCTURES”. Ann. Sofia Univ. Fac. Math. and Inf. 90 (December 12, 1998): 91–108. Accessed November 24, 2024. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/288.