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Check

… that Or gadget implements the 3-way disjunction

\begin{equation*} \ell_1 \lor \ell_2 \lor \ell_3. \end{equation*}

The Or gadget:

0ceb40bf-4e47-4aee-89db-b404445c4ee1.svg

No coloring exists when \(\ell_1 = \ell_2 = \ell_3 = 0\):

\(\ell_1\) \(\ell_2\) \(\ell_3\) \(c_1\) \(c_2\) \(c_3\) \(c_4\) \(c_5\)
0 0 0 n/a 1 2 2 0
0 0 0 n/a 2 2 1 0
0 0 0 1 n/a 2 2 0
0 0 0 2 n/a 2 1 0
0 0 0 1 2 n/a 0 2
0 0 0 2 1 n/a 0 2
0 0 0 1 2 2 n/a 0
0 0 0 2 1 2 n/a 0
0 0 0 1 2 2 0 n/a
0 0 0 2 1 2 0 n/a

Otherwise, a coloring exists:

\(\ell_1\) \(\ell_2\) \(\ell_3\) \(c_1\) \(c_2\) \(c_3\) \(c_4\) \(c_5\)
0 0 1 1 2 0 0 2
0 0 1 2 1 0 0 2
0 1 0 1 0 2 2 0
0 1 0 2 0 2 1 0
0 1 1 2 0 0 1 2
0 1 1 2 0 2 1 0
1 0 0 0 1 2 2 0
1 0 0 0 2 2 1 0
1 0 1 0 2 0 1 2
1 0 1 0 2 2 1 0
1 1 0 0 2 2 1 0
1 1 0 2 0 2 1 0
1 1 1 0 2 0 1 2
1 1 1 0 2 2 1 0
1 1 1 2 0 0 1 2
1 1 1 2 0 2 1 0

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