. . . "b.2 H groups.It is preferred that T is H.It is preferred that R.sup.1 is H or methyl, especially H.Examples of preferred optionally substituted phenyl and naphthyl groups represented by A are 4-carboxyphenyl, 3-carboxyphenyl, 3,5-dicarboxyphenyl, 3,4-dicarboxyphenyl, 2-methyl-5-carboxyphenyl, 2-sulpho-5-carboxyphenyl, 6-carboxynaphth-1-yl,7-carboxynaphth-1-yl, 6-carboxynaphth-2-yl and 1-sulpho-6-c" .