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In page Kazhdan's property (T):

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*Grigory Margulis used the fact that SL(n, Z) (for n ≥ 3) has property (T) to construct explicit families of expanding graphs, that is, graphs with the property that every subset has a uniformly large "boundary". This connection led to a number of recent studies giving an explicit estimate of Kazhdan constants, quantifying property (T) for a particular group and a generating set. *Alain Connes used discrete groups with property (T) to find examples of type II1 factors with countable fundamental group, so in particular not the whole of positive reals ℝ+. Sorin Popa subsequently used relative property (T) for discrete groups to produce a type II1 factor with trivial fundamental group.