وَيَخْتَصُّ «لَا» بِالنَّكِرَةِ، وَيَعُمُّ «مَا» بِالْمَعْرِفَةِ وَالنَّكِرَةِ.
Translation: In this construction, lā is restricted to an indefinite ism, whereas mā can govern either a definite or an indefinite ism.
This indefinite-only condition refers specifically to lā resembling laysa. We will contrast it with lā of generic negation later in this lesson.