The interrogative hamzah may come before لَمْ: أَ + لَمْ = أَلَمْ.
أَلَمْ تَعْلَمْ؟ — Did you not know?
The hamzah makes the expression a question. لَمْ still gives past negation and the following imperfect remains Mudari Akhaff.
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Interrogative Hamzah with Lam
The interrogative hamzah may come before لَمْ: أَ + لَمْ = أَلَمْ.
أَلَمْ تَعْلَمْ؟ — Did you not know?
The hamzah makes the expression a question. لَمْ still gives past negation and the following imperfect remains Mudari Akhaff.