Shuffling and unshuffling
Henshall, D. , N. Rampersad, and J. Shallit. “Shuffling and unshuffling.” Bulletin of the European Association of Theoretical Computer Sciece 107 (2012): 131-142.
We consider various shuffling and unshuffling operations on languages and words, and examine their closure properties. Although the main goal is to provide some good and novel exercises and examples for undergraduate formal language theory classes, we also provide some new results and mention some open problems.