A multiplicative characterization of the power means
  A startlingly simple characterization of the p-norms has recently been found by Aubrun and Nechita (arXiv:1102.2618) and by Fernandez-Gonzalez, Palazuelos and Perez-Garcia. We deduce a simple characterization of the power means of order greater than or equal to 1. 
Tom Leinster
math.FA cs.IT math.CA math.IT