  The partial entanglement entropy (PEE) $s_{\mathcal{A}}(\mathcal{A}_i)$
characterizes how much the subset $\mathcal{A}_i$ of $\mathcal{A}$ contribute
to the entanglement entropy $S_{\mathcal{A}}$. We find one additional physical
requirement for $s_{\mathcal{A}}(\mathcal{A}_i)$, which is the invariance under
a permutation. The partial entanglement entropy proposal satisfies all the
physical requirements. We show that for Poincar\'e invariant theories the
physical requirements are enough to uniquely determine the PEE (or the
entanglement contour) to satisfy a general formula. This is the first time we
find the PEE can be uniquely determined. Since the solution of the requirements
is unique and the \textit{PEE proposal} is a solution, the \textit{PEE
proposal} is justified for Poincar\'e invariant theories.
