Degree(u) returns the syntactic degree of the univariate polynomial over power series u with respect to its main variable. That is, it doesn't test whether the highest degree coefficient is nonzero (because this cannot be done in general); it just returns the highest degree coefficient of the main variable that is specified.

When using the MultivariatePowerSeries package, do not assign anything to the variables occurring in the power series and univariate polynomials over power series. If you do, you may see invalid results.

$\mathrm{with}\left(\mathrm{MultivariatePowerSeries}\right)\:$

$f≔\mathrm{UnivariatePolynomialOverPowerSeries}\left(1+x^{3}y+xyz+\left(1+y\right)z^2\,z\right)\:$

$\mathrm{Degree}\left(f\right)$

$2$

$g≔\mathrm{UnivariatePolynomialOverPowerSeries}\left(\left[\mathrm{PowerSeries}\left(x\right)\,\mathrm{PowerSeries}\left(y\right)\,\mathrm{GeometricSeries}\left(\left[x\right]\right)\,\mathrm{PowerSeries}\left(0\right)\right]\,u\right)\:$

$\mathrm{Degree}\left(g\right)$

$3$

The MultivariatePowerSeries[Degree] command was introduced in Maple 2021.

For more information on Maple 2021 changes, see Updates in Maple 2021.