functions (rn) generate a subspace isomorphic to ℓ2. We consider the space Λ (R, X) of
measurable functions f such that fg∈ X for every function g=∑ bnrn where (bn)∈ ℓ2. We
show that if X satisfies certain conditions on the fundamental function and on certain
interpolation indices then the space Λ (R, X) is not order isomorphic to a rearrangement
invariant space. The result includes the spaces Lp, q and certain classes of Orlicz and …