The Clerk's Slip

Very Hard — logic-grid deduction puzzle

Helios, Borealis, Meridian and Aquila waited out on the piers, and one line of the night's logbook was wrong.

On clear nights, the harbour observatory rolled its four telescopes out onto the piers. The piers stood in a row along the water, numbered one to four. Helios, Borealis, Meridian and Aquila each got a pier of their own, a mirror coating and a filter, and the night clerk wrote it all down in the logbook before the lamps went out. Tonight the clerk came over red in the face. One line in the logbook was wrong. Which one? The clerk wouldn't say. The sky was clearing fast, visitors were already lining up, and somebody had to set things right.

Clues

1. Helios stood somewhere before Borealis along the row of piers.
2. Walking from the first pier to the fourth, a visitor passed Borealis before Meridian, and Meridian before Aquila.
3. The pier numbers of the gold coating and the comet filter added up to six.
4. The nebula filter was further along the row than the sun filter.
5. Logbook line A: the platinum coating was on the pier right after the gold coating.
6. Logbook line B: Aquila was on an earlier pier than Meridian.
7. Logbook line C: the rhodium coating and the gold coating were on piers next to each other.
8. Only one of logbook lines A, B and C was wrong, and the other two were right.
9. Going along the row, the nebula filter came exactly one pier after the moon filter.

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