An almost unit is a nonunit in the integral domain of formal power series with a nonzero first
coefficient, 
,
where 
. Under the operation of composition,
the almost units in the integral domain of formal power series over a field 
form a group
(Henrici 1988, p. 45).
Almost Unit
See also
Schur-Jabotinsky TheoremExplore with Wolfram|Alpha
References
Henrici, P. Applied and Computational Complex Analysis, Vol. 1: Power Series-Integration-Conformal Mapping-Location of Zeros. New York: Wiley, p. 45, 1988.Referenced on Wolfram|Alpha
Almost UnitCite this as:
Weisstein, Eric W. "Almost Unit." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/AlmostUnit.html