أَوْ تَقْدِيرًا، نَحْوُ: «غُلَامُ زَيْدٍ»؛ تَقْدِيرُهُ: «غُلَامٌ لِزَيْدٍ».
Translation: Or the prepositional relationship is understood, as in “Zayd’s servant”; its sense is “a servant belonging to Zayd.”
غُلَامُ is the mudāf; its own case depends on its role in the sentence.
زَيْدٍ is the mudāf ilayh, genitive in the construction.
The imagined lām explains the relationship; it is not an overt preposition inserted into the actual construct phrase.