أَنْتُمَا تَكْتُبَانِ — لَنْ تَكْتُبَا — لَمْ تَكْتُبَا
The second-person dual follows the same nūn-retention/deletion pattern; its alif does not disappear.
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Dual Second Person: Three Moods
Four Patterns of Imperfect Mood Marking
أَنْتُمَا تَكْتُبَانِ — لَنْ تَكْتُبَا — لَمْ تَكْتُبَا
The second-person dual follows the same nūn-retention/deletion pattern; its alif does not disappear.