= Normalized Marsden dual functional
{title2=$\lambda_i(p)=\sum_{j=0}^{k-1}(-1)^jp^{(j)}(x)\psi_i^{(k-1-j)}(x)$}
When the knot polynomial is normalized as $\psi_i(x)=\prod_{\ell=1}^{k-1}(x-t_{i+\ell})/(k-1)!$, the displayed formula has no additional factorial prefactor. Applied to <Marsden's identity>, it extracts the coefficient of the corresponding <B-spline> in any polynomial of degree at most $k-1$. Differentiating the finite sum makes adjacent terms cancel, proving independence of $x$. For linear polynomials the coefficient is their value at the <Greville abscissa>.
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