A square is contained in its concentric doubled square.
The circumscribed closed disc is contained in the concentric doubled square; this is the geometric reason certified re-entry must double.
The structural invariant actually required of a worklist component: there is a first square and every square has its precision. Connectivity is an algorithmic optimization and is not needed by soundness.
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The union of the closed squares retained by a component.
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The initial Cauchy component is a nonempty singleton component.
Component-level restatement of executable Cauchy coverage.
The executable enclosing square contains the union of all input squares, without a common-precision or connectivity hypothesis.
The doubled enclosing square used by NK certification contains the whole input component region.
The certified region selected by an atom certificate. Reflected certificates preserve the region kind of their source certificate.
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The region whose root count is asserted by a certified result.
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The root count carried by a certified result.
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Every certificate claims at least one root.
Re-entry always constructs a nonempty common-precision component.
Re-entry preserves candidate-count positivity; together with
toComponent_wellFormed this is the loop kernel's re-entry contract.
The doubled square retained on re-entry contains the certified region, for both atom certificate forms and for clusters.
Re-entry contains the stored square, independently of certificate form.
Re-entry contains the stored circumscribed disc, independently of certificate form. This stronger conservative fact is useful to the loop kernel, which need not inspect the atom-witness disjunction.
The worklist region of toComponent contains the certified region.