Christol–André conjecture on globally bounded D-finite power series

Let y(x)=k0akxkQ[[x]]y(x)=\sum_{k\geq 0}a_kx^k\in\mathbb{Q}[[x]] be D-finite. Assume that the sequence (ak)k0(a_k)_{k\geq 0} has at most geometric growth, that there exists NNN\in\mathbb{N} such that y(Nx)y(0)Z[[x]]y(Nx)-y(0)\in\mathbb{Z}[[x]], and that, in the minimal-order monic linear differential equation satisfied by y(x)y(x), x=0x=0 is not a pole of any coefficient ai(x)a_i(x). Christol–André conjecture. Then y(x)y(x) is algebraic. This conjecture proposes an arithmetic strengthening of Eisenstein's theorem: suitable integrality and growth conditions, together with a regularity condition at the origin, should force a D-finite series to be algebraic. The source presents it as open; it also mentions a variant replacing the third condition by the absence of logarithms in the local solutions at x=0x=0.

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Primary source

Alin Bostan, Xavier Caruso and Julien Roques, “Algebraic solutions of linear differential equations: an arithmetic approach”, arXiv:2304.05061 (2024).

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