Dutch national flag problem

Also called sort colors, three-way partition problem, three-way partitioning problem.

Partition an array of three values into three contiguous blocks in one pass with O(1) extra space.

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The build computes these levels from the evidence in the repository. Each row says what the next level needs. Read what the levels mean.

Ladder	Level	What the next level needs
Human proof	H0 no proof	add a proof in proofs/ (06.5)
Lean	L0 no Lean part	name a Lean module in the lean field (07)
Visual	V0 none	add viz/scene.ts or a figure (10)
Writing	W0 stub	Definition one source with a locator