  When sufficient numbers of holes are introduced into the two-dimensional CuO2
square lattice, dynamic magnetic correlations become incommensurate with
underlying lattice in all previously investigated La_{2-x}A_xCu_{1-z}B_zO_{4+y}
(A=Sr or Nd, B=Zn) including high T_C superconductors and insulators, and in
bilayered superconducting YBa_2Cu_3O_{6.6} and Bi_2Sr_2CaCu_2O_8. Magnetic
correlations also become incommensurate in structurally related La_2NiO_4 when
doped with Sr or O. We report an exception to this so-far well established
experimental "rule" in La_2Cu_{1-z}Li_{z}O_4 in which magnetic correlations
remain commensurate.
