A Compactness Theorem for Surfaces with Lp-Bounded Second Fundamental Form. Joel Langer — 1985 Mathematische Annalen
Diffeomorphisms of the Circle and Geodesic Fields on Riemannian Surfaces of Genus One. Joel Langer; David A. Singer — 1982 Inventiones mathematicae
Recursion in curve geometry. Langer, Joel — 1999 The New York Journal of Mathematics [electronic only]