وَلَا يَجِبُ ذَلِكَ فِي عَكْسِهِ، وَلَا فِي الْمُتَجَانِسَيْنِ.
Translation: The adjective is not obligatory in the reverse case or when the two terms belong to the same definiteness class.
Reverse: an indefinite antecedent followed by a definite badal.
Same class: both definite or both indefinite.
The source limits the requirement; do not extend it to every badal.
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Badal: Definition, Four Types, and Parsing
وَلَا يَجِبُ ذَلِكَ فِي عَكْسِهِ، وَلَا فِي الْمُتَجَانِسَيْنِ.
Translation: The adjective is not obligatory in the reverse case or when the two terms belong to the same definiteness class.
Reverse: an indefinite antecedent followed by a definite badal.
Same class: both definite or both indefinite.
The source limits the requirement; do not extend it to every badal.