Raşa, I. “Strictly Concave and Strictly Superharmonic Functions”.
Anal. Numér. Théor. Approx.
15, no. 1 (February 1, 1986): 69–74. Accessed April 14, 2025.
https://ictp.acad.ro/jnaat/journal/article/view/1986-vol15-no1-art10
.