- Alexander D. Popov, Martin Wolf, “Hidden Symmetries and Integrable Hierarchy of the ${\mathcal{N}}$ = 4 Supersymmetric Yang-Mills Equations”, Commun. Math. Phys., 275, № 3, 2007, 685
- Ling-Lie Chau, “Linear systems and conservation laws of gravitational fields in four plus extended superspace”, Physics Letters B, 202, № 2, 1988, 238