  In a system of n quantum particles, we define a measure of the degree of
irreducible n-way correlation, by which we mean the correlation that cannot be
accounted for by looking at the states of (n-1) particles. In the case of
almost all pure states of three qubits we show that there is no such
correlation: almost every pure state of three qubits is completely determined
by its two-particle reduced density matrices.
