Abstract
We consider, in rings of formal power series, the series whose coefficients, in a certain sense, “tends to infinity”. In this manner, we determine subrings of the rings as above, which have several derivations. Some of these subrings are composition rings also. At first, we study direct products of groupoids.
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Notes
For us, \(\mathbb {N}_0\) is the set of all natural numbers, while \(\mathbb {N}\) is the set of natural numbers, \(0\) excluded.
For \(\alpha \in B\), in a homogeneous component of \(\alpha \), only a finite number of elements of \(T\) effectively appears.
We can read: \(n\) is the order of \(\alpha \) with respect to \(I\).
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This work was supported by GNSAGA of INdAM.
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Gallina, G., Morini, F. Subgroupoids of some direct products and formal power series. Beitr Algebra Geom 56, 387–396 (2015). https://doi.org/10.1007/s13366-014-0191-9
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DOI: https://doi.org/10.1007/s13366-014-0191-9