Case 2: The three close pairs form a path: \( AB, BC, CD \). Edges: AB, BC, CD. Trio \( A,B,C \): AB, BC close â†’ 2 close pairs. Trio \( B,C,D \): BC, CD close â†’ 2 close pairs. Trio \( A,B,D \): AB, BD? BD not close, AD not close â†’ only AB â†’ 1 close â†’ fails. Trio \( A,C,D \): AC not close â†’ 0 â†’ fails. So only the two middle trios (A,B,C) and (B,C,D) each have exactly 2 close pairs.

Fri, 08 May 2026 10:59:17 +0000

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