1. N = 4 topological strings
2. Vanishing Theorems for the Self-Dual N = 2 String;Berkovits;San Paulo preprint IFUSP-P-1134,1994
3. Loop Amplitudes of N = 2 Strings;Ooguri,1995
4. Twisting the N = 2 String, DESY and Hannover preprint;Ketov;DESY 93–191, ITP-UH-24/93,1993