Result 122, Theoretical computer science

Quantitative trace-reconstruction bounds with a uniform decoder

At every fixed deletion probability in (0,1)(0,1), reconstructing an arbitrary length-n binary string requires nΩ(log⁡log⁡n)n^{\Omega(\log\log n)} independent traces, ruling out polynomial-sample reconstruction. A uniform decoder achieves quasipolynomial sample and running-time bounds for known fixed rational retention probabilities. When the deletion probability is at most n−εn^{-\varepsilon} for fixed ε > 0, both bounds become polynomial in the input and parameter encoding.

Lean formalization New or sharp bound

The bigger picture

Why it matters

Trace reconstruction asks how to recover a binary string from independent copies with bits randomly deleted but the survivors kept in order. These manuscripts claim limits on how much evidence is needed, alongside an algorithm that uses it.

What changes?

The uniform-decoder manuscript reports an algorithm for every binary string, given its length n and rational retention probability, the chance each bit survives. At each fixed retention probability between zero and one, samples and bit-operation costs are quasipolynomial: bounded by n raised to a fixed power of log n. Success probability is at least two-thirds per string. When deletion probability is at most n to the power minus epsilon, for fixed positive epsilon, both bounds become polynomial in input and parameter encoding.

What does that help mathematicians do?

The lower-bound manuscript claims that, at every fixed deletion probability strictly between zero and one, worst-case reconstruction needs at least n raised to a positive constant times log log n samples. This holds even with unrestricted computation and any fixed positive success probability. It rules out polynomial-sample methods for arbitrary binary strings: faster computation alone cannot overcome insufficient evidence. The upper and lower bounds do not establish an optimal rate.

Are there practical applications?

The immediate value is foundational: uniformity makes the retention probability an input rather than requiring a separate algorithm for each value. The reported running time is polynomial in the sample budget and binary input length. This makes reconstruction guarantees computationally explicit, but the superpolynomial worst-case sample requirement prevents interpreting them as immediately practical at fixed deletion rates.

This section was generated by GPT-6 Astra Medium. This explanation is based on the result summary and manuscript abstracts below. This context is separate from OpenAI's source text.

3 manuscripts

Uniform quasipolynomial-time trace reconstruction

October 5, 2026 29 pages

We give a uniform algorithm that reconstructs every binary string from independent deletion traces when its length and rational retention probability are known. For each fixed retention probability, both the number of traces and the bit complexity are quasipolynomial in the string length. More generally, we give an explicit sample bound uniform over all rational retention probabilities, with running time polynomial in the sample budget and the binary input length. If the deletion probability is at most n−εn^{-\varepsilon} for fixed ε > 0, the sample and running-time bounds are polynomial. Reconstruction succeeds with probability at least 2/3 for each input string.

Cite (BibTeX)
@misc{OAI:Uniform-quasipolynomial-time-trace-reconstruction-October-5-2026,
  author = {{OpenAI}},
  title = {{Uniform quasipolynomial-time trace reconstruction}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Uniform-quasipolynomial-time-trace-reconstruction-October-5-2026/uniform-trace-reconstruction.pdf}{OAI:Uniform-quasipolynomial-time-trace-reconstruction-October-5-2026}},
  year = {2026}
}

A latest-anchor induction with spectrally compact masks for worst-case trace reconstruction

October 5, 2026 15 pages

We give an improved worst-case sample bound for reconstructing a string from independent deletion traces, with its length and retention probability known. For each fixed retention probability, the number of traces is quasipolynomial: the logarithm of the sample budget is O((log⁡n)3(1+log⁡log⁡(2n))6)O((\log n)^3(1+\log\log(2n))^6). If the deletion probability is at most n−εn^{-\varepsilon} for fixed ε > 0, polynomially many traces suffice. These bounds apply to binary strings and to strings of general symbols observed exactly. They concern sample complexity and do not assert an efficient reconstruction algorithm or matching optimality.

Cite (BibTeX)
@misc{OAI:A-latest-anchor-induction-with-spectrally-compact-masks-for-worst-case-trace-reconstruction-October-5-2026,
  author = {{OpenAI}},
  title = {{A latest-anchor induction with spectrally compact masks for worst-case trace reconstruction}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/A-latest-anchor-induction-with-spectrally-compact-masks-for-worst-case-trace-reconstruction-October-5-2026/paper.pdf}{OAI:A-latest-anchor-induction-with-spectrally-compact-masks-for-worst-case-trace-reconstruction-October-5-2026}},
  year = {2026}
}

Quantitative lower bounds for trace reconstruction

September 24, 2026 42 pages

Exact worst-case reconstruction of a binary word from independent deletion traces requires nΩ(log⁡log⁡n)n^{\Omega(\log\log n)} samples for every fixed deletion probability q∈(0,1)q\in(0,1), even with unrestricted computation and any fixed positive success probability. This gives a negative answer to the polynomial-sample question for binary trace reconstruction. More generally, when q3log⁡n→∞q^3\log n\to\infty, we prove a lower bound of nclog⁡(q3log⁡n)n^{c\log(q^3\log n)} samples for every fixed 0<c<1/(4log⁡2)0\lt c\lt 1/(4\log2). Here q is the known deletion probability, and all logarithms are natural.

Cite (BibTeX)
@misc{OAI:quantitative-lower-bounds-for-trace-reconstruction-September-24-2026,
  author = {{OpenAI}},
  title = {{Quantitative lower bounds for trace reconstruction}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/quantitative-lower-bounds-for-trace-reconstruction-September-24-2026/paper.pdf}{OAI:quantitative-lower-bounds-for-trace-reconstruction-September-24-2026}},
  year = {2026}
}

Lean formalization

OpenAI's note on what the formalization covers, from lean/docs/122.md.

Quantitative trace-reconstruction bounds with a uniform decoder

The following describes the scope of the Lean formalization related to the following accompanying paper(s):

Scope

The formalization proves superpolynomial sample lower bounds for exact worst-case reconstruction of binary words from independent deletion traces, with unrestricted computation and any fixed positive success probability. For every fixed deletion probability q∈(0,1)q\in(0,1), sample complexity grows faster than every fixed power of the word length; the minimum total-variation distance between two one-trace laws decays faster than every inverse power.

More quantitatively, along sequences with q3log⁡n→∞q^3\log n\to\infty, the required number of samples is at least nclog⁡(q3log⁡n)n^{c\log(q^3\log n)} eventually for every fixed 0<c<1/(4log⁡2)0<c<1/(4\log2). All logarithms are natural.

Comparator links

Result Comparator statement
Quantitative and superpolynomial sample lower bounds for trace reconstruction TraceReconstruction.lean

Data from github.com/openai/math at commit adc7f12, committed October 6, 2026 at 21:58 UTC, last checked for changes about 9 hours ago. Titles, subjects, summaries, abstracts and Lean notes are OpenAI's; page counts are read from the PDFs. The map, related results, search, kinds of results and the named-problem index are Emergent Mind's, built with text embeddings and an LLM, and may contain errors.

An Emergent Mind Labs project. Emergent Mind is not affiliated with OpenAI. None of these results has been peer reviewed. Cite the manuscripts themselves, using the BibTeX on each result's page.