1. A. Polyakov, The wall of the cave, hep-th/9809057.
2. J. Maldacena, The large N limit of superconformal field theories and supergravity, hep-th/9711200.
3. A. Giveon, D. Kutasov and N. Seiberg, Comments on string theory on AdS3, hep-th/9806194.
4. J. Rahmfeld and A. Rajaraman, The GS string action on AdS3 × S3 with Ramond-Ramond charge, hep-th/9809164.
5. Igor Pesando, The GS Type IIB Superstring action on AdS3 × S3 × T4 hep-th/9809145.