@article{NUMA_1989__56_2-3_133415,
     author = {Shangyou Zhang},
     title = {An {Optimal} {Order} {Multigrid} {Method} for {Biharmonic,} {C1} {Finite} {Element} {Equations.}},
     journal = {Numerische Mathematik},
     pages = {613--624},
     publisher = {mathdoc},
     volume = {56},
     number = {2-3},
     year = {1989},
     zbl = {0667.65089},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1989__56_2-3_133415/}
}