  Quantum teleportation can be performed if and only if a message is combined
with a maximally entangled state. Bennett et al. originally claimed this
feasibility condition. In this paper, I give a proof of that condition.
Moreover, I specify the condition for teleportation when a single-qubit message
is combined with a three-qubit state distributed among three parties. I also
consider the situation that a single-qubit message is combined with an
$n$-qubit state distributed among $n$ parties.
