Hasse Diagrams for Attention: A Partial Order Framework for Designing Transformer Masks

Chentao Li; Han Guo

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arXiv · 2606.09951

Hasse Diagrams for Attention: A Partial Order Framework for Designing Transformer Masks

Chentao Li·Han Guo

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Abstract

During the training of large Transformer models, attention masks regulate the scope and direction of information flow across a sequence. Numerous mask variants exist, and operators such as FlexAttention already support arbitrary attention masks. Nevertheless, a systematic formal analysis of the information-flow structure induced by arbitrary masks has been missing. This paper develops a complete theoretical framework. We prove that, with sufficient depth, the information flow of a multi-layer Transformer converges to a Hasse diagram -- a directed acyclic graph representing a partial order. Building on this, we recast the design of parallel training tasks as the problem of finding a minimal common supergraph of Hasse diagrams, and we establish a criterion for the minimal common supergraph. This yields a constructive method to derive attention masks directly from a family of tasks. Applying the framework, we design two novel masks: a block-generation attention mask that ensures training-inference consistency (Block Two-Stream Attention), and a fully supervised bidirectional attention mask (Butterfly Attention). These results demonstrate the framework's capacity to discover new structures.

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Chentao Li, Han Guo. 2026-06-08. Hasse Diagrams for Attention: A Partial Order Framework for Designing Transformer Masks. https://arxiv.org/abs/2606.09951

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