1. A. M. Vershik and S. I. Karpushev, “Cohomology of groups in unitary representations, the neighborhood of the identity, and conditionally positive definite functions,” Mat. Sb., 119:4 (1982), 521–533; English transl.: Math. USSR-Sbornik, 47 (1984), 513–526.
2. Y. Shalom, “Rigidity of commensurators and irreducible lattices,” Invent. Math., 141:1 (2000), 1–54.
3. B. Bekka, P. de la Harpe, and A. Valette, Kazdan’s Property (T), Cambridge University Press, Cambridge, 2007.
4. U. Haagrup, “An example of nonnuclear C*-algebra, which has the metric approximation property,” Invent. Math., 50:3 (1978), 279–293.
5. P.-A. Cherix et al., Groups with the Haagerup Property: Gromov’s A-T-Menability, Birkhäuser Verlag, Basel, 2001.