The Billaud Conjecture for ${|{ varSigma } |} = 4$, and Beyond. - Szymon Lopaciuk; Daniel Reidenbach (DLT, 2022)

On Billaud words and their companions. - Szymon Lopaciuk; Daniel Reidenbach (Theor. Comput. Sci., 2023)

The Billaud Conjecture for alphabet size 4. - Szymon Lopaciuk; Daniel Reidenbach (Inf. Comput., 2025)