“The Semi-Global Isometric Imbedding in R3 of Two Dimensional Riemannian Manifolds With Gaussian Curvature Changing Sign Cleanly”. Journal of Partial Differential Equations 6, no. 1 (June 1, 1993): 62–79. Accessed February 26, 2026. https://global-sci.com/index.php/jpde/article/view/3735.