Every year, I teach the Modern Geometries course at my University. As one part of that course, we study transformational geometry, concluding with explorations of the seven frieze patterns and the seventeen wallpaper patterns.
To create a sense of realism, I bring in large piles of examples of friezes and wallpapers from sample books graciously supplied by local home design companies. The students seem to enjoy coding the "group" name for each pattern, and gain considerable experience looking for centers of rotation, lines of reflections, and translation vectors.
This fall, I decided to update my supply of examples. But, to my dismay, none of the local design companies carried wallpaper patterns any more. One owner claimed she had not sold any wallpaper for more than two years, and had recycled all of her sample books.
What should I do? Are wallpaper patterns no longer a relevant example of transformational geometry? I suppose I can still bring in examples from past cultures, but it just does not make sense to study "wallpaper patterns" when my students know about as much about wallpaper as they do about long-playing records.
Yes, the times are changing! Next year, I guess we will study the seventeen "wrapping paper" patterns....