Mrinal Kumar, Shubhangi Saraf. The limits of depth reduction for arithmetic formulas: it's all about the top fan-in. In David B. Shmoys, editor, Symposium on Theory of Computing, STOC 2014, New York, NY, USA, May 31 - June 03, 2014. pages 136-145, ACM, 2014. [doi]
Abstract is missing.