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Published online by Cambridge University Press: 16 April 2025
Let f be a non-constant meromorphic function. We define its linear differential polynomial $ L_k[f] $ by
\begin{equation*}L_k[f]=\displaystyle b_{-1}+\sum_{j=0}^{k}b_jf^{(j)}, \text{where}\; b_j (j=0, 1, 2, \ldots, k) \; \text{are constants with}\; b_k\neq 0.\end{equation*}
$ L_k[f] $. Furthermore, we study the Fermat-type functional equations of the form
$ f^n+g^n=1 $ to find the meromorphic solutions (f, g) which enable us to answer the question of Li completely. This settles the long-standing open problem of Li.
Present address: Department of Mathematics, Jadavpur University, Kolkata, India.