The local minima of the free energy of a quasi one-dimensional electron sys
tem with short-range repulsion on a lattice were found which correspond wit
h the symmetry-allowed matching pairs of the precursor CDW and SDW modulati
on periods, possible relation of the theory to the `staircase' instabilitie
s in the doped nickelates with perovskite structure is discussed. (C) 1998
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