1. G S Setlur and Y C Chang,Phys. Rev. B57, 15144 (1998)
2. F D M Haldane,Phys. Lett. A93, 464 (1983);Phys. Rev. Lett. 50, 1153 (1983)
3. H J Schulz, G Cuniberti and P Pieri, inField theories for low dimensional condensed matter systems edited by G Morandi, A Tagliacozzo and P Sodano (Springer, Berlin, 2000), cond-mat/9807366
4. H J Schulz, inProceedings of Les Houches Summer School LXI edited by E Akkermans, G Montambaux, J Pichard and J Zinn-Justin (Elsevier, Amsterdam, 1995), cond-mat/9503150
5. G S Setlur and D S Citrin,Phys. Rev. B65, 165111 (2002)