  Cirel'son inequality states that the absolute value of the combination of
quantum correlations appearing in the Clauser-Horne-Shimony-Holt (CHSH)
inequality is bound by $2 \sqrt 2$. It is shown that the correlations of two
qubits belonging to a three-qubit system can violate the CHSH inequality beyond
$2 \sqrt 2$. Such a violation is not in conflict with Cirel'son's inequality
because it is based on postselected systems. The maximum allowed violation of
the CHSH inequality, 4, can be achieved using a Greenberger-Horne-Zeilinger
state.
