9.1 More wave propagation around obstructions
When a wave has a choice of paths by which to reach a given destination, we have seen in Chapter 8 that the components add or subtract according to their relative phases upon arrival. When the number of contributing paths is small, we generally refer to their interference; when the number is large, it is more common to describe this as diffraction.
Pain  pp. 366–407French  pp. 284–298Main  pp. 320–339Hecht  Chapter 10Lipson et al.  Chapter 8Feynman  Vol. I, Chapter 30
As Feynman remarks in his Lectures on Physics, however, ‘no one has ever been ...