On metric characterizations of some classes of Banach spaces
  The paper contains the following results and observations: (1) There exists a sequence of unweighted graphs $\{G_n\}_n$ with maximum degree 3 such that a Banach space $X$ has no nontrivial cotype iff $\{G_n\}_n$ admit uniformly bilipschitz embeddings into $X$; (2) The same for Banach spaces with no nontrivial type; (3) A sequence $\{G_n\}$ characterizing Banach spaces with no nontrivial cotype in the sense described above can be chosen to be a sequence of bounded degree expanders; (4) The infinite diamond does not admit a bilipschitz embedding into Banach spaces with the Radon-Nikod\'{y}m property; (5) A new proof of the Cheeger-Kleiner result: The Laakso space does not admit a bilipschitz embedding into Banach spaces with the Radon-Nikod\'{y}m property; (6) A new proof of the Johnson-Schechtman result: uniform bilipschitz embeddability of finite diamonds into a Banach space implies its nonsuperreflexivity. 
Mikhail Ostrovskii
math.FA math.MG