Why doesn lateral inversion apply vertically?
A deeper (but still basically very simple): Any object that does not have a plane of symmetry is said to be chiral (in chemistry the term and the concept is often applied to molecules, and is especially important in biochemistry and pharmacology). When you view a chiral object in a mirror, the image that you see has the chirality reversed. Thus, for example, you look like someone with hair parted on the left, whereas yours is actually parted on the right. This is called “lateral inversion”. It is an unfortunate and misleading term, as it seems to suggest a sideways inversion, i.e. that left and right are interchanged in the image that we see, which certainly does not happen in the sense of shifting from one side to the other (see above). The reversal of chirality is the complete story – there’s really nothing more to be said about it. No question about the image being turned upside-down should arise.
