The lām in al-kitābu li-Zaydin indicates possession; in jiʾtu li-l-dirāsati it indicates purpose. Neither is additional.
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Original Lām: Ownership and Purpose
Additional Particles: Seven Forms, Emphasis and Syntactic Case
The lām in al-kitābu li-Zaydin indicates possession; in jiʾtu li-l-dirāsati it indicates purpose. Neither is additional.