Six persons A, B, C, D, E and F sit in two rows of three persons each. If E is…

Concept: In a two-row seating arrangement where the rows face each other, the seat in column position i of one row sits directly opposite the seat in column position i of the other row (leftmost opposite leftmost, middle opposite middle, rightmost opposite rightmost). "Diagonally opposite" means the far-corner seat of the other row — the left end of one row is diagonally opposite the right end of the other row, and vice versa. Only the two outer seats of a row of three are "ends"; the middle seat is not an end.

Application:

1. D is second to the left of F: in a row of exactly three seats, this places D and F at the two ends of the same row with exactly one seat between them.

2. B is the neighbor of F: F is at an end of the D–F row, so F's only same-row neighbor is the middle seat. That middle seat must therefore be B, giving the row D–B–F.

3. The remaining three people, A, C and E, occupy the other row.

4. E is not at any end: in a row of three this forces E into the middle seat of the other row.

5. C is the neighbor of E: since E holds the middle seat, C must sit at one of the two end seats of that row, leaving A at the other end.

6. C sits diagonally opposite D: D is at an end of the D–B–F row, so its diagonal partner is the far-corner (opposite) end seat of the other row. Fixing C there also fixes A at the remaining end, in the same column as D.

7. The two rows are now fixed — Row 1: D, B, F; Row 2 (aligned by column): A, E, C — and each seat faces the seat in the same column of the other row.

Since B occupies the middle seat of Row 1 and E occupies the middle seat of Row 2, and middle seats of facing rows sit in the same column, B sits directly opposite E.

Cross-check: B's seat is pinned purely by "neighbor of F" (the only open seat next to F), and E's seat is pinned purely by "not at any end" (the only non-end seat in its row) — two independent constraints that both land on the middle seats of the two rows. Because middle seats always face each other directly, this independently confirms B and E are opposite each other, without needing to resolve the diagonal C–D relationship at all.