[3] Aslani, H., Salkuyeh, D. K., Beik, F. P. A.: 
On the preconditioning of three-by-three block saddle point problems. Filomat 15 (2021), 5181-5194. 
DOI 10.2298/FIL2115181A | 
MR 4394237[11] Huang, N., Dai, Y.-H., Hu, Q.: 
Uzawa methods for a class of block three-by-three saddle-point problems. Numer. Linear Algebra Appl. 26 (2019), Article ID e2265, 26 pages. 
DOI 10.1002/nla.2265 | 
MR 4033762 | 
Zbl 1463.65046[14] Huang, Z.-G., Wang, L.-G., Xu, Z., Cui, J.-J.: 
An efficient preconditioned variant of the PSS preconditioner for generalized saddle point problems. Appl. Math. Comput. 376 (2020), Article ID 125110, 26 pages. 
DOI 10.1016/j.amc.2020.125110 | 
MR 4068949 | 
Zbl 1474.65063[18] Salkuyeh, D. K., Aslani, H., Liang, Z.-Z.: 
An alternating positive semidefinite splitting preconditioner for the three-by-three block saddle point problems. Math. Commun. 26 (2021), 177-195. 
MR 4297389 | 
Zbl 07424441[19] Wang, L., Zhang, K.: 
Generalized shift-splitting preconditioner for saddle point problems with block three-by-three structure. Open Access Library J. 6 (2019), Article ID e5968, 13 pages. 
DOI 10.4236/oalib.1105968 | 
MR 3615979[20] Wang, N.-N., Li, J.-C.: 
On parameterized block symmetric positive definite preconditioners for a class of block three-by-three saddle point problems. J. Comput. Appl. Math. 405 (2022), Article ID 113959, 15 pages. 
DOI 10.1016/j.cam.2021.113959 | 
MR 4355119 | 
Zbl 1480.65067