  The notion of distillable entanglement is one of the fundamental concepts of
quantum information theory. Unfortunately, there is an apparent mismatch
between the intuitive and rigorous definitions of distillable entanglement. To
be precise, the existing rigorous definitions impose the constraint that the
distilation protocol produce an output of constant dimension. It is therefore
conceivable that this unnecessary constraint might have led to underestimation
of the true distillable entanglement. We give a new definition of distillable
entanglement which removes this constraint, but could conceivably overestimate
the true value. Since the definitions turn out to be equivalent, neither
underestimation nor overestimation is possible, and both definitions are
arguably correct
