FA-40228 / Heap invariants / Member archive

Skew meld retains a unary subtree instead of misclassifying the winner as a leaf · case 03

The bounded skew meld step certificate reports an incorrect leaf.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

A skew meld unwind chooses the smaller root, recursively melds its old right subtree with the other heap, and unconditionally swaps children. Record supplies winner, old_left, recursive_result and sizes. Missing subtrees are None. No rank-based swap condition is part of this model.

Why this case matters

This isolates an internal heap representation or priority-structure invariant using deterministic finite records.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression certificate 3	`{"leaf": true, "new_left": 3, "new_right": null, "preorder_children": [3], "rewrites": [[3, 9]], "size": 5}`	`{"leaf": false, "new_left": 3, "new_right": null, "preorder_children": [3], "rewrites": [[3, 9]], "size": 5}`	Failed

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