سَقَرُ has three letters and its middle letter is vowelled; the taught rule includes it. For هِنْدٌ / هِنْدُ, Arabic permits both declension and diptote treatment. Thus this three-letter Arabic feminine name with a sakin middle is not obligatorily ghayr munsarif under the stated conditions.
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Three Letters: The Middle Letter Matters
Cause of Ghayr Munsarif: Feminine Alif and Feminine Proper Names
سَقَرُ has three letters and its middle letter is vowelled; the taught rule includes it. For هِنْدٌ / هِنْدُ, Arabic permits both declension and diptote treatment. Thus this three-letter Arabic feminine name with a sakin middle is not obligatorily ghayr munsarif under the stated conditions.