Illustration: Alan Stonebraker

Figure 1: (Top left) Many-particle systems exhibit complex, messy entanglement structures. (Top right) Entanglement combing straightens out the correlations among the parties so that ebits are created between Alice and each of the Bobs individually. A curly line on the right stands for one ebit, hence $n1=3$, $n2=1$, $n3=2$, and $n4=1$ in this example. (Bottom left) The initial entangled state of Alice, Bob, and Charlie is $|ψ〉ABC$. If $S(B|A)≤0$, then Bob can transfer (or merge) his state to Alice by sending classical messages only. (Bottom right) In addition to the successful transfer, Alice and Bob will share $-S(B|A)$ ebits at the end of the protocol; in the displayed example we have $-S(B|A)=2$.