A note on the zeroth products of Frenkel-Jing operators

Quantum vertex algebra theory, developed by H.-S. Li, allows us to apply zeroth products of Frenkel-Jing operators, corresponding to Drinfeld realization of $U_q (\widehat{\mathfrak{sl}}_{n+1})$, on the extension of Koyama vertex operators. As a result, we obtain an infinite-dimensional space and describe its structure as a module for the associative algebra $U_q (\mathfrak{sl}_{n+1})_z$, a certain quantum analogue of $U(\mathfrak{sl}_{n+1})$ which we introduce in this paper.