@ARTICLE{Kimball2021, title = {{E}vidence for {H}ierarchical {B}lack {H}ole {M}ergers in the {S}econd {LIGO}-{V}irgo {G}ravitational {W}ave {C}atalog}, status = {}, author = {Kimball, C. and Talbot, C. and Berry, C.P.L. and Zevin, M. and Thrane, E. and Kalogera, V. and Buscicchio, R. and Carney, M. and Dent, T. and Middleton, H. and Payne, E. and Veitch, J. and Williams, D.}, journal = {Astrophysical Journal Letters}, volume = {915}, pages = {}, year = {2021}, }