6.5. References 235
Exercise 6.4.3. Let r be a discrete group with property (T). Show that
r is residually finite if and only if there exists an embedding of r into the
unitary group of the hyperfinite II 1 -factor R.^14
6.5. References
Theorem 6.2. 7 comes from [105], though our proof is found in [134]. The
main results in Section 6.4 are also due to Kirchberg [105].
14Robertson has generalized this result (of Kirchberg) by replacing R with any II1 -factor
with the Haagerup approximation property ([166]).