What is the force of “in” in “in yattabiʿūna illā al-ẓann”?

Rhetorical Addition: Emphasis, Explanatory Coordination, Connections and Multiple Meanings

• “In” introduces a condition with an omitted answer
• “In” is a reduced emphatic particle
• Negation, followed by restriction with “illā”
• “In” only affirms instead of negating