Official rule text
61.6 A player can score a maximum of one public objective and one 61.17 SECRET OBJECTIVES secret objective during each status phase. A secret objective is an objective that is controlled by one player and is hidden from all
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Source: Twilight Imperium: Fourth Edition - Living Rules Reference: Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 61.6