The morphic structure conjecture for L(2)

Let L(w)L(w) denote the lexicographically least infinite word on N\mathbb{N} beginning with ww whose only square factors are contained in the prefix ww. Let L(ε)L(\varepsilon) be the corresponding word with empty prefix, and let γ\gamma be the morphism defined by

γ(0)=c3c3+,\gamma(0)=c_3c_3^+,

and, for n0n\geq 0,

γ(n)=R4b4+  R5b5+Rn+2bn+2+  Rn+3bn+3,\gamma(n)=R_4b_4^+\;R_5b_5^+\cdots R_{n+2}b_{n+2}^+\;R_{n+3}b_{n+3},

where the words bnb_n, cnc_n, and RnR_n are defined recursively in the paper. The morphic structure conjecture for L(2)L(2).

L(2)=2γ(L(ε)).L(2)=2\gamma(L(\varepsilon)).

This conjecture proposes an explicit morphic description of the lexicographically least square-free extension beginning with 22, analogous to the established descriptions for L(1)L(1) and L(n)L(n) with n3n\geq 3.

Sources & referencesView supporting material

Primary source

Siddharth Berera, Andrés Gómez-Colunga, Joey Lakerdas-Gayle, John López, Mauditra Matin, Daniel Roebuck, Eric Rowland, Noam Scully and Juliet Whidden, “The lexicographically least square-free word with a given prefix”, arXiv:2210.00508 (2022).

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