Morphisms and extensions between bricks over preprojective algebras of type A

Abstract

The bricks over preprojective algebras of type A are known to be in bijection with certain combinatorial objects called "arcs". In this paper, we show how one can use arcs to compute bases for the Hom-spaces and first extension spaces between bricks. We then use this description to classify the "weak exceptional sequences" over these algebras. Finally, we explain how our result relates to a similar combinatorial model for the exceptional sequences over hereditary algebras of type A.

arXiv commentv3: accepted manuscript. v2: additional references to related work, corrected an error in the proof of Proposition 6.6. 26 pages, 11 figures

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