Vladeva, D. “Properties of the Maximum Likelihood Estimation of Constant Drift and Diffusion Parameters in $k$-Dimensional Diffusion Process Observed at Discrete Random Sampling”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 93, Dec. 2001, pp. 61-71, https://ftl5.uni-sofia.bg/index.php/fmi/article/view/204.