What is the khabar of mā and lā resembling laysa?

لَيْسَ raises its noun and puts its khabar into nasab. Some uses of مَا and لَا copy it exactly, and when they do, the reporting word goes into nasab with them.

مَا سَعِيدٌ جَالِسًا (mā sa'īdun jālisan) — Sa'īd is not sitting. سَعِيدٌ is the ism, marfū'; جَالِسًا is the khabar, manṣūb.

لَا رَجُلَ حَاضِرًا (lā rajula ḥāḍiran) — no man is present.

They copy لَيْسَ exactly: the noun stays in rafa, the khabar drops into nasab.

The governing is fragile. It is cancelled outright in three situations, and the sentence then reverts to a plain mubtada' and khabar, both marfū':

when the khabar comes after إِلَّا — مَا زَيْدٌ إِلَّا قَائِمٌ; when the khabar is brought forward before the noun — مَا قَائِمٌ زَيْدٌ; when إِنْ is added after مَا — مَا إِنْ خَالِدٌ نَازِلٌ.

This governing is the usage of the people of Ḥijāz. Banū Tamīm do not let مَا govern at all, and read the khabar in rafa throughout.

Do not confuse this لَا with the لَا of absolute negation.

The لَا that resembles لَيْسَ leaves its noun in rafa and puts its khabar in nasab — لَا رَجُلٌ حَاضِرًا.

The لَا لِنَفْيِ الْجِنْسِ does the opposite: its noun is manṣūb with a bare fatḥa and no tanwīn, and its khabar stays marfū' — لَا رَجُلَ حَاضِرٌ.

One letter apart in writing; opposite endings on both words.