functions in slice3.i - t

             to_corners(list, ni, nj)  
 
     convert a LIST of cell indices in an (NI-1)-by-(NJ-1)-by-(nk-1)  
     logically rectangular grid of cells into the list of  
     2-by-2-by-2-by-numberof(LIST) cell corner indices in the  
     corresponding NI-by-NJ-by-nk list of vertices.  
interpreted function, defined at i/slice3.i   line 488