In the active heavy-nūn paradigm, the three masculine third-person positions are:
Word / formMeaning / explanation
لَيَفْعَلَنَّthird masculine singular
لَيَفْعَلَانِّthird masculine dual
لَيَفْعَلُنَّthird masculine plural
The singular has fatḥa before the nūn, the dual retains the alif and has a kasrah on the doubled nūn, and the masculine plural has ḍamma immediately before it.
One man will certainly do; two men will certainly do; the men will certainly do. All three begin with third-person yāʾ, so the ending identifies their number.