Given the following statement: "A plane wave is incident (from the free space) upon a semi-infinite medium made of N=100 different lossless dielectric slabs." Visually/spatially, what does this look like? I can see two possibilities 1) the slabs are stacked on top of each other, like plates stacked on a table, and the wave incident from the side(horizontally). 2) the slabs are stacked like a row of books on a shelf, and the wave is incident upon the flat plane of the first dielectric, thus penetrating each slab one by one from one side to the other. Are any of these two possibilities correct ways of interpretating the statement above?