From earlier levels, recall that particles can change the ending of an imperfect verb. Lam al-Amr makes it akhaff/jussive.
Ending groupResult with Lam al-AmrExampleFirst group: 5 slots ending on the root consonant, without inflectional nūnfinal sukunيَكْتُبُ ← لِيَكْتُبْSecond group: 7 slots ending in inflectional nūninflectional nūn is removedيَسْمَعُونَ ← لِيَسْمَعُواThird group: 2 feminine-plural slots ending in pronominal nūnform remains unchangedيَكْتُبْنَ ← لِيَكْتُبْنَ
These are ending groups, not person categories such as third, second and first person.