Kurylev, Yaroslav, and Matti Lassas. “Multidimensional Gel’fand Inverse Boundary Spectral Problem: Uniqueness and Stability”. CUBO, A Mathematical Journal 8, no. 1 (April 1, 2006): 41–59. Accessed January 28, 2026. https://cubo.ufro.cl/index.php/cubo/article/view/1611.