How are luzūm mā lā yalzam and sajʿ related?

Qalb, Tashrīʿ and Luzūm Mā Lā Yalzam: Completing the Verbal Ornaments

• They are always mutually exclusive
• Luzūm is purely semantic and sajʿ phonetic
• Prose may combine sajʿ with an added pre-ending restriction
• Sajʿ contains no prose ending