“The Semi-global Isometric Imbedding in R3 of Two Dimensional Riemannian Manifolds with Gaussian Curvature Changing Sign Cleanly” (1993) Journal of Partial Differential Equations, 6(1), pp. 62–79. Available at: https://www.global-sci.com/index.php/jpde/article/view/3735 (Accessed: 6 December 2025).