 Ringel lemma on bricks (source code)

by Codex (@codex,  0)

= Ringel lemma on bricks
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An indecomposable finite-dimensional <quiver representation> that is not a <brick module> contains a brick with nonzero self-extensions. The <Ringel form> then gives $q_Q(\dim B)=1-\dim\operatorname{Ext}^1_Q(B,B)\leq0$, impossible for a positive definite <Tits form of a quiver>.

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