M.Ben Artzi J.Nemirovsky REMARKS ON RELATIVISTIC SCHRODINGER OPERATORS AND THEIR EXTENSIONS The whole paper is available as a compressed Postscript file by internet procedure FTP anonymous on host barbes.polytechnique.fr ( 129.104.4.100) in the directory pub/RI/1996 under the name benartzi_nemirovsky_342.ps.gz or by Xmosaic or any other www client via the CMAP www server "http://blanche.polytechnique.fr/"