1. W. Siegel, Two vierbein formalism for string inspired axionic gravity, Phys. Rev. D 47 (1993) 5453 [ hep-th/9302036 ] [ INSPIRE ].
2. W. Siegel, Superspace duality in low-energy superstrings, Phys. Rev. D 48 (1993) 2826 [ hep-th/9305073 ] [ INSPIRE ].
3. W. Siegel, Manifest duality in low-energy superstrings, in Proceedings of Strings’93, Berkeley, 1993, pg. 353, hep-th/9308133 [ INSPIRE ].
4. M. Duff, Duality Rotations in String Theory, Nucl. Phys. B 335 (1990) 610 [ INSPIRE ].
5. J. Maharana and J.H. Schwarz, Noncompact symmetries in string theory, Nucl. Phys. B 390 (1993) 3 [ hep-th/9207016 ] [ INSPIRE ].