REVIEW 3 major objections 6 minor 3 cited by
Learning Euler Factors of Elliptic Curves
T0 review · 3 major / 6 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read An encoder-only transformer trained on Frobenius traces $a_q$ for $q<100$, $q\neq p$ predicts $a_p \bmod 2$ with around $0.94$ accuracy and MCC around $0.84$ for most primes $p<100$, without access to L-functions or functional equations.
desk verdict A promising ML-plus-number-theory proof-of-concept whose headline accuracies are compromised by an unmeasured train/test overlap on repeated input tuples. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the Frobenius trace $a_p(E) = p + 1 - |E(\mathbb{F}_p)|$, the coefficient in the local Euler factor $1/(1 - a_p p^{-s} + p^{1 - 2s})$. The argument is carried by an encoder-only transformer whose vocabulary tokenizes signed integers; it reads the sequence $(a_q)_{q\neq p,\ q<100}$ and is trained, in the parity experiments, on targets reduced modulo $2$. Two auxiliary mechanisms are essential: the dataset of isogeny classes with conductors below $10^7$, and the modulo-2 duplicate-removal and balancing procedure that separates the training and test sets. The interpretability step uses PCA of token embeddings and of decoder hidden states to show that the model organizes its representations by residues modulo $2$ and $4$.
What would settle it
Build the test set for the $a_p \bmod 2$ task by discarding every input tuple $(a_q)_{q\neq p,\ q<100}$ that also appears in training, then retrain; if accuracy on that tuple-disjoint test set is near $0.5$, the claimed parity learning is an artifact of overlap.
Extended reading notes
Core claim
On the paper's own terms, the central discovery is that a transformer can learn the arithmetic of Frobenius traces from data alone. For the exact-value task, $a_{97}$ is predicted with test MCC $0.4711$ against a most-common-class baseline of $0.082$, and the model captures $|a_{97}|$ better than the sign (sign-agnostic MCC $0.6266$); $a_2$ and $a_3$ show the same pattern. When the target is reduced modulo $2$, the encoder-only transformer reaches accuracies close to $0.94$ and MCCs around $0.84$ for most primes $p<100$ (accuracy $0.9472$ at $p=83$, MCC $0.8703$ at $p=5$), with the lowest results at $p=2$. The authors read this as evidence that the model implicitly computes $a_p \bmod 2$ as an intermediate step, and they corroborate it by showing confusion matrices consistent with parity classes and PCA projections of embeddings and decoder hidden states that cluster by residues modulo $2$, $4$, and in one case $6$.
Load-bearing premise
The empirical claim rests on the assumption that test accuracy measures learning of new input sequences rather than recall of sequences already seen during training.
Editorial extensions
If this is right
- If the central claim is correct, a neural network can recover the parity of a missing Euler factor from its neighbors in a regime where no efficient deterministic completion algorithm is known.
- The parity signal is the model's main strength, and exact-value predictions inherit it: models trained on exact $a_p$ already predict $a_p \bmod 2$ with MCC near the models trained directly on the parity task.
- The sign of $a_p$ is the principal obstacle; the sign-agnostic MCC exceeds the full MCC in every exact-value experiment.
- The pattern is stable across the dataset range: results on a test set with conductors up to $10^7$ remain well above chance, though the highest conductor band $10^6$--$10^7$ is the least accurate.
Reading between the lines
- Read together with the paper's own Section 4.2, which reports that reducing inputs modulo 2 makes over 80% of test tuples appear in training, the Section 3 exact-value results motivate a tuple-disjoint retest before concluding the model generalizes to genuinely unseen sequences.
- If the parity result survives the tuple-disjoint retest, the PCA-visible parity structure could be used to generate explicit conjectural congruences among Frobenius traces for verification by traditional Galois-representation methods.
- The parity prediction task may be equivalent, in effect, to learning the mod-2 Galois representation attached to the curve; the paper's embedding evidence suggests the model finds this representation before it finds the full trace.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper trains encoder-only transformers and feedforward neural networks on datasets of isogeny classes of elliptic curves over Q (conductors up to 10^7) to predict Frobenius traces a_p, or their residues mod 2, from traces at other small primes q < 100. The main empirical claims are that exact a_p prediction for p = 97 reaches accuracy 0.4923 against a baseline of 0.082, that a_p mod 2 prediction from a_q mod 2 reaches accuracies near 0.94 and MCC near 0.84, and that PCA and saliency analyses suggest the models implicitly learn mod-2 and mod-4 structure. The paper interprets these results as evidence that neural networks can learn relationships among Euler factors without explicit number-theoretic tools such as functional equations.
Significance. If the quantitative claims are robust, this is a useful experimental data point for the machine-learning/number-theory interface: it would show that standard transformer architectures can pick up congruence structure in Frobenius traces and expose it in learned embeddings. The paper is also explicit about some limitations, such as the overlap problem for mod-2 inputs. However, the strength of the claims depends critically on whether test accuracy measures generalization to genuinely new input tuples, and the current manuscript does not establish this for the exact-trace experiments. The PCA and saliency sections are suggestive but informal; they do not by themselves carry the central quantitative claim.
major comments (3)
- [§3.1, §3.2, §4.1, §4.2] The train/test split is by isogeny class, not by the input tuple (a_q)_{q<100, q≠p}. Section 4.2 demonstrates that this distinction matters: after reducing inputs modulo 2, more than 80% of the test data appears in the training set, and the authors had to remove duplicates before reporting results. For the exact-trace experiments in Sections 3 and 4.1, no duplicate removal or overlap statistic is reported. If identical input tuples recur in both training and test, then the reported accuracies and MCCs (e.g., a_97 accuracy 0.4923 in Table 1, parity accuracies near 0.94 in Figure 5) may reflect memorization of tuple-to-label mappings rather than generalization to new trace sequences. The authors should quantify, for each experiment, the fraction of test tuples that also occur in the training set, and should report results after deduplication or after explicitly removing overlapping tuples from the test set.
- [Table 1, Table 3, Figure 5, Figure 6] The paper reports 'maximum' test accuracy and 'maximum' test MCC obtained during training, but it does not specify whether the checkpoint used for evaluation was selected on a validation set or on the test set. Selecting the best epoch by test performance inflates the reported numbers and makes the results non-reproducible without additional protocol details. The authors should report early stopping on a validation split, or else provide the full training curve and state explicitly that the maximum is over validation epochs. In addition, no repeated-seed experiments or confidence intervals are reported, so it is unclear how stable the numbers in Table 1 and Figure 5 are.
- [§4.2] The handling of indeterminate cases after duplicate removal is ambiguous. The text says that the dataset is balanced and that between 5% and 11.5% of the training set consists of indeterminate cases (same input tuple with different a_p mod 2 labels). It is not stated whether the test set likewise contains indeterminate cases, nor how predictions are scored when the input admits two valid labels. If indeterminate cases are present in the test set, the achievable accuracy is bounded by the majority fraction for those tuples, and reporting accuracy without separating deterministic and indeterminate inputs makes the parity results difficult to interpret. The authors should specify the evaluation rule and report results separately for deterministic and indeterminate test cases.
minor comments (6)
- [§2.4.2] There is a typo: 'the the Mathews correlation coefficient' should be 'the Matthews correlation coefficient', and the attribution should be to Matthews.
- [Figure 5 caption] The caption contains a stray '5,' in 'The highest MCC, 5, 0.8703'; this should read 'The highest MCC, 0.8703'.
- [§1 and §3.1] The introduction says models predict a_97 from a_q with q < 97, whereas Section 3.1 specifies the input as (a_q)_{q≠p, q≤100}; these descriptions should be reconciled.
- [§5] The convention 'a ≡ b (mod 0) ⇔ a = b' is nonstandard and should be explained more clearly in the main text rather than in a footnote-like parenthetical.
- [Table 3] The caption 'Primes excluded' is unclear: it should state explicitly that the model's input excludes a_q for the listed primes while predicting a_97 from the remaining a_q values.
- [References] The reference [AHL+] is listed as 'In preparation'; if it is used as context, the authors should provide a stable reference or remove it.
Circularity Check
No significant circularity: reported predictions are measured on held-out isogeny classes and no derived quantity is reused as an input.
full rationale
The paper's central claim is empirical: transformers and feedforward networks predict Frobenius traces and their parities from neighboring traces, with accuracies reported on data reserved as isogeny classes distinct from training (Section 3.1 and Section 4.1). This is a direct measurement rather than a construction that reuses the target as an input. The mathematical motivation cites Serre's theorem and related results, but the ML predictions do not assume those theorems; they are evaluated against Sutherland's ECQ6/ECQ7 databases. Self-citations to Int2Int and prior ML-number-theory papers are tooling or related-work references and are not load-bearing. The paper itself flags a genuine limitation in Section 4.2: after reducing inputs modulo 2, more than 80% of test tuples occur in training, and it removes duplicates for those experiments. For full-trace experiments, no duplicate removal is reported, so the magnitudes of the reported accuracies could in principle be affected by tuple overlap; this is an experimental-validity caveat, not a circular derivation. The claimed ability to learn Euler-factor structure is therefore not equivalent by construction to the training inputs, and no circular step can be identified from the text.
Assumptions & free parameters
free parameters (2)
- Neural network parameters =
4,223,805 trainable parameters (encoder-only transformer); FFN sizes vary, up to 1,709,353
- Training hyperparameters =
learning rates 3e-5 and 5e-5; 100 to 1,000 epochs; embedding dim 256; 8 heads; 4 layers; batch sizes 100,000…
assumptions (5)
- standard math Hasse bound |a_p| <= 2*sqrt(p) gives finite label sets for a_2, a_3, a_97 used as classification targets.
- domain assumption Serre's theorem that, under the Riemann hypothesis for Artin L-functions, finitely many Frobenius traces determine the isogeny class of a Q-nonisogenous, non-CM elliptic curve.
- domain assumption The Sutherland ECQ6/ECQ7 datasets faithfully represent isogeny classes of elliptic curves over Q with conductor less than 10^6 and 10^7, with correctly computed traces.
- domain assumption In the mod-2 experiments, the tuple (a_q mod 2)_{q<100, q!=p} almost always determines a_p mod 2; the small fraction of indeterminate cases is kept rather than excluded.
- ad hoc to paper The 24-prime window q<100, q!=p is sufficient input for the models to identify the relevant mod-2 Galois representation for most curves in the dataset.
Cite this review
Pith. "Pith review of Learning Euler Factors of Elliptic Curves." pith.science (2026). https://pith.science/paper/6HXGPTDN
@misc{pith2026250210357,
author = {Pith},
title = {Pith review of: Learning Euler Factors of Elliptic Curves},
year = {2026},
howpublished = {\url{https://pith.science/paper/6HXGPTDN}},
note = {Machine review of arXiv:2502.10357}
}
abstract
We apply transformer models and feedforward neural networks to predict Frobenius traces $a_p$ from elliptic curves given other traces $a_q$. We train further models to predict $a_p \bmod 2$ from $a_q \bmod 2$, and cross-analysis such as $a_p \bmod 2$ from $a_q$. Our experiments reveal that these models achieve high accuracy, even in the absence of explicit number-theoretic tools like functional equations of $L$-functions. We also present partial interpretability findings.
Figures
Figures from the paper (10 more)
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Reviewed August 7, 2026 · model on record in the stance chip above.
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