Unbounded ladders induced by Gorenstein algebras
  The derived category of a Gorenstein triangular matrix algebra $A$ admits an unbounded ladder, which is of period $3$ if $A = T_2(B)$. Also, a left recollement of triangulated categories with Serre functors sits in a ladder of period $1$; as an application, the singularity category of $A$ admits a ladder of period $1$. 
Pu Zhang, Yuehui Zhang, and Lin Zhu
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