  It is shown that within the framework of application of the general scheme of
the Landau theory of phase transitions to the magnetic crystals the equilibrium
and stable equal-module exchange structures automatically appears in addition
to the other magnetic states. No additional conditions such as the existence of
the Andreev-Marchenko spin scalar are needed. Furthermore, they are not
constrained by the dimensionality of irreducible representation as it typically
takes place for the Andreev-Marchenko-type structures.
