“The Semi-global Isometric Imbedding in R3 of Two Dimensional Riemannian Manifolds with Gaussian Curvature Changing Sign Cleanly”, J. Part. Diff. Eq., vol. 6, no. 1, pp. 62–79, Jun. 1993, Accessed: Dec. 06, 2025. [Online]. Available: https://www.global-sci.com/index.php/jpde/article/view/3735