Transformer Heads Looking for Order

arXiv:2609.25588 · cs.AI, cs.LG · Submitted 2026-09-22 · Read on arXiv

cs.AI, cs.LG

Submitted: 2026-09-22

Updated: 2026-09-22

License: http://creativecommons.org/licenses/by/4.0/

The gist: In this note, we show that the problem of checking, whether a sequence of bits is ordered, is not doable by 1-head 1-layer transformers but is doable by a 2-head 1-layer transformer.

Terminology

Abstract

In this note, we show that the problem of checking, whether a sequence of bits is ordered, is not doable by 1-head 1-layer transformers but is doable by a 2-head 1-layer transformer. Unlike similar previous results, our results assume the model where transformers have an output MLP.

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