invertible formal power series
Theorem. Let be a commutative ring with non-zero unity. A formal power series
(1) |
is invertible in the ring iff is invertible in the ring .
Proof. . Let have the multiplicative inverse . Since
we see that , i.e. is an invertible element (unit) of .
. Assume conversely that is invertible in . For making from a formal power series
(2) |
the inverse of , we first choose . For all already defined coefficients let the next coefficient be defined as
This equation means that
vanishes for all ; since , the product of the formal power series (1) and (2) becomes simply equal to 1. Accordingly, is invertible.
Title | invertible formal power series |
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Canonical name | InvertibleFormalPowerSeries |
Date of creation | 2016-04-27 10:47:14 |
Last modified on | 2016-04-27 10:47:14 |
Owner | pahio (2872) |
Last modified by | pahio (2872) |
Numerical id | 8 |
Author | pahio (2872) |
Entry type | Theorem |
Classification | msc 13H05 |
Classification | msc 13F25 |
Classification | msc 13J05 |
Related topic | RulesOfCalculusForDerivativeOfFormalPowerSeries |