Lemma 13.4.7. Let \mathcal{D} be a pre-triangulated category. Let f : X \to Y be a morphism of \mathcal{D}. There exists a distinguished triangle (X, Y, Z, f, g, h) which is unique up to (nonunique) isomorphism of triangles. More precisely, given a second such distinguished triangle (X, Y, Z', f, g', h') there exists an isomorphism
(1, 1, c) : (X, Y, Z, f, g, h) \longrightarrow (X, Y, Z', f, g', h')
Proof. Existence by TR1. Uniqueness up to isomorphism by TR3 and Lemma 13.4.3. \square
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