1. Monge-Ampère Equations;T. Aubin,1982
2. Berger, M. S.: Nonlinearity and Functional Analysis. Academic Press, New York, 1977.
3. Milnor, T. K.: Harmonic Maps and Classical Surface Theory in Minkowski 3-Space. Transactions of the A.M.S. 280, 1 (1983).
4. O'Neill, B.: Semi-Riemannian Geometry, Academic Press, New York, 1982.
5. Palmer, B.: On a Theorem of Lawson (in preparation).