A Haskell SmirnovWordsModule.hs module exporting six functions for calculating
the numbers of Smirnov words over three-letter and four-letter alphabets in the
theoretical framework of the breakthrough article
H. Prodinger, Ternary Smirnov words and generating functions, Integers, 2018, 18,
Paper A69.
Based on the two Remarks made in Appendix A of the monograph A.O. Matveev, Symmetric Cycles, Jenny Stanford Publishing, 2023. See the accompanying PDF-note.
Smirnov words are words without consecutive equal letters.