يَقِيَانِ → لَنْ يَقِيَا / لَمْ يَقِيَا
Translation: The two protect → The two will not / did not protect.
يَقِينَ → لَنْ يَقِينَ / لَمْ يَقِينَ
Translation: They (fem.) protect → They will not / did not protect.
The first loses indicative nūn, while the second retains feminine-plural nūn, a pronoun marker. Identical letter names do not imply identical grammatical roles.
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Indicative Nūn and Feminine-Plural Nūn
Complete Paradigm of the Separated Doubly Weak Verb وَقَى يَقِي
يَقِيَانِ → لَنْ يَقِيَا / لَمْ يَقِيَا
Translation: The two protect → The two will not / did not protect.
يَقِينَ → لَنْ يَقِينَ / لَمْ يَقِينَ
Translation: They (fem.) protect → They will not / did not protect.
The first loses indicative nūn, while the second retains feminine-plural nūn, a pronoun marker. Identical letter names do not imply identical grammatical roles.