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Table tab:n21 records, for each of the six duals: not an intertwining tree; Even Level Graph source (duals 1,2 only); and bridge-switch path length to an ELG (0,0 for the two ELG-outright cases; 3,1,2,4 for the rest). All six are bridge-derived; all witnesses step-verified. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>