  It is well known that (non-orthogonal) pure states cannot be cloned so one
may ask: how much or what kind of additional (quantum) information is needed to
supplement one copy of a quantum state in order to be able to produce two
copies of that state by a physical operation? For classical information, no
supplementary information is required. However for pure quantum
(non-orthogonal) states, we show that the supplementary information must always
be as large as it can possibly be i.e. the clone must be able to be generated
from the additional information alone, independently of the first (given) copy.
