1. L. Belarbi, On the symmetries of the Sol₃ Lie group, J. Korean. Math. Soc. 57 (2) (2020), 523-537.
2. R. Caddeo, S. Montaldo, C. Oniciuc and P. Piu, The classification of biharmonic curves of Cartan-Vranceanu 3-dimensional spaces, The 7th Int. Workshop on Dif. Geo. and its Appl., Cluj Univ. Press, Cluj-Napoca, (2006), 121-131.
3. R. Caddeo, S. Montaldo and P. Piu, Biharmonic curves on a surface. Rend. Mat. Appl. 21 (2001), 143-157.
4. R. Caddeo, C. Oniciuc and P. Piu, Explicit formulas for non-geodesic biharmonic curves of the Heisenberg group, Rend. Sem. Mat. Univ. Politec. Torino. 62 (2004), 265-27
5. B.-Y. Chen and S. Ishikawa, Biharmonic surfaces in pseudo-Euclidean spaces, Mem. Fac. Sci. Kyushu Univ. Ser. A 45 (2) (1991), 323--347.