Akpan D, “Singularities of two-dimensional Nijenhuis operators”, European Journal of MathematicsThis link is disabled., 8:4 (2022), 1328–1340
Akpan D., “Almost Differentially Nondegenerate Nijenhuis Operators”, Russian Journal of Mathematical PhysicsThis link is disabled., 29:4 (2022), 413–416
Akpan D., Oshemkov A., “Elementary Differential Singularities of Three-Dimensional Nijenhuis Operators”, Russian Journal of Mathematical Physics, 30:4 (2023), 425–431