In this case, $w(R)=2^0=1$. We have two adjacent vertex subsets, $v s_{d_1}$ and $v s_{d_2}$, with $d_1$ adjacent to $d_2$. The size of each vertex subset is at most $w(R)+1=2$, so the size of their union is at most $2+2=4$.
Now, let's consider the case where
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