  The generalized n-qubit Greenberger-Horne-Zeilinger (GHZ) states and their
local unitary equivalents are the only pure states of n qubits that are not
uniquely determined (among arbitrary states, pure or mixed) by their reduced
density matrices of n-1 qubits. Thus, the generalized GHZ states are the only
ones containing information at the n-party level.
