Clarify conditions for bounds interpolation

ch08.adoc

@@ -587,7 +587,7 @@ given by the **`tie_point_mapping`** attribute.
 [[compression-by-coordinate-subsampling-interpolation-of-cell-boundaries, Section 8.3.9, "Interpolation of Cell Boundaries"]]
 ==== Interpolation of Cell Boundaries
 
-Coordinates may have cell bounds. Equivalently to the way coordinates can be stored as coordinate tie points and reconstituted through interpolation, contiguous cell bounds of interpolated dimensions can be stored as __bounds tie points__ and reconstituted through interpolation. In this process, the coordinate tie points are a prerequisite for the bounds tie points and the same interpolation method used for the coordinate interpolation is used for the bounds interpolation.
+Coordinates may have cell bounds. For the case that the reconstituted cells are contiguous and have exactly two cell bounds along each interpolated dimension, cell bounds of interpolated dimensions can be stored as __bounds tie points__ and reconstituted through interpolation. In this process, the coordinate tie points are a prerequisite for the bounds tie points and the same interpolation method used for the coordinate interpolation is used for the bounds interpolation.  
 
 For the reconstituted coordinates, cell bounds are stored separately for each coordinate point, as shown in the left part of <<figure_interpolation_of_cell_boundaries>>
 for the example of 2D bounds. Since the cell bounds are contiguous, bounds points of adjacent cells will coincide and so the full set of bounds points may be represented as a grid, comparable to the coordinate points grid. In the middle part of <<figure_interpolation_of_cell_boundaries>>