Ah ha! Yes, I thought so.
“A decoupling lemma”
“The first of several lemmas that will be used to prove the quantum capacity theorem concerns a phenomenon known as decoupling. Informally speaking, this is the phenomenon whereby the action of a sufficiently noisy channel on a randomly chosen subspace of its input space can be expected not only to destroy entanglement with a secondary system, but to destroy classical correlations as well. The lemma that follows proves a fact along these lines that is specialized to the task at hand. “