= Cubic B-spline Bézier extraction
For the unit-spaced cubic cardinal <B-spline> on $[0,4]$, the four scalar cubic <Bernstein basis> coefficient rows are $(0,0,0,1/6)$, $(1/6,1/3,2/3,2/3)$, $(2/3,2/3,1/3,1/6)$ and $(1/6,0,0,0)$. Each row applies on its interval with local parameter in $[0,1]$. They result from the compactly supported $C^2$ truncated-cube combination $\tfrac16\sum_{j=0}^4(-1)^j\binom4j(x-j)_+^3$. Each graph piece is a cubic <Bézier curve> with abscissa controls $j,j+1/3,j+2/3,j+1$.
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