  If Z is a quotient of a subspace of a separable Banach space X, and V is any
separable Banach space, then there is a Banach couple (A_0,A_1) such that A_0
and A_1 are isometric to $X\oplus V$, and any intermediate space obtained using
the real or complex interpolation method contains a complemented subspace
isomorphic to Z. Thus many properties of Banach spaces, including having
non-trivial cotype, having the Radon-Nikodym property, and having the analytic
unconditional martingale difference sequence property, do not pass to
intermediate spaces.
