The two verbs can show different visible jussive results because each follows its own ending group.
● Final sukun: تَدْرُسُ ← تَدْرُسْ and تَنْجَحُ ← تَنْجَحْ.
● Inflectional nun removed: يَجْلِسُونَ ← يَجْلِسُوا.
● No visible change with nun an-niswah: تَكْتُبْنَ ← تَكْتُبْنَ.
So إِنْ يَجْلِسُوا نَبْدَأْ is correct: the first verb loses its inflectional nun, while the second ends in sukun.
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Conditional Sentences with إِنْ
The two verbs can show different visible jussive results because each follows its own ending group.
● Final sukun: تَدْرُسُ ← تَدْرُسْ and تَنْجَحُ ← تَنْجَحْ.
● Inflectional nun removed: يَجْلِسُونَ ← يَجْلِسُوا.
● No visible change with nun an-niswah: تَكْتُبْنَ ← تَكْتُبْنَ.
So إِنْ يَجْلِسُوا نَبْدَأْ is correct: the first verb loses its inflectional nun, while the second ends in sukun.