to 3 d show a layer structure involving a layer normal ay having two maximal values and a component cz having three minimal values and two maximal values simultaneously changing the signs of the coordinate axes of the ay and cz will not change the generality of the structure fig4 a to 4 d show a layer structure involving a layer normal ay having two maximal values and a minimal value and a component cz having two maximal values and three minimal values when the ay crosses 0 the layer structure causes a kink fig5 a to 5 d show a layer structure involving a layer normal ay having no extreme values and a component cz having a minimal value fig6 a to 6 d show a layer structure that resembles the layer structure of fig5 but is asymmetrical fig7 a to 7 d show a layer structure involving a layer normal ay having two inflection points and a component cz having a minimal value fig8 a to 8 d show a layer structure involving a layer normal ay having a minimal value on one side and a component cz having two maximal values fig9 a to 9 d show a layer structure involving a layer normal ay having a minimal value and a component cz having a minimal value fig1 a to 10 d show a layer structure involving a layer normal ay having a minimal.