The two forms are easiest to distinguish by the inserted weak letter.
Main added featureExampleBab
Initial ت + و between 2nd and 3rd root lettersتَسَرْوَلَ6
Initial ت + ي between 1st and 2nd root lettersتَخَيْعَلَ7
Their Masdars are تَسَرْوُلٌ and تَخَيْعُلٌ.
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Attached Derived Quadrilateral - Bab 6: Tafallul & Bab 7: Tafay'ul
The two forms are easiest to distinguish by the inserted weak letter.
Main added featureExampleBab
Initial ت + و between 2nd and 3rd root lettersتَسَرْوَلَ6
Initial ت + ي between 1st and 2nd root lettersتَخَيْعَلَ7
Their Masdars are تَسَرْوُلٌ and تَخَيْعُلٌ.