Rule 1: 1. لَا followed directly by an indefinite noun
When لَا that denies absolutely is immediately followed by an indefinite noun, that noun takes the accusative and loses its tanwīn: لَا كِتَابَ عَلَى الْمَائِدَةِ there is no book on the table. A plural behaves the same way: لَا رِجَالَ هُنَا there are no men here. If the noun is the first term of an iḍāfa it is an ordinary accusative, with its full ending: لَا طَالِبَ عِلْمٍ كَسْلَانُ no seeker of knowledge is lazy. A definite noun or a verb after لَا is simply negated in the ordinary way: لَا الرَّجُلُ حَضَرَ وَلَا الْمَرْأَةُ, لَا أَعْرِفُ.
لَا رَجُلَ فِي الْبَيْتِ.
lā rajula fi l-bayti
There is no man in the house.
لَا فَرْقَ بَيْنَ غَنِيٍّ وَفَقِيرٍ فِي الصَّفِّ.
lā farqa bayna ghaniyyin wa-faqīrin fi ṣ-ṣaffi
There is no difference between rich and poor in the row.
لَا كُتُبَ فِي هٰذِهِ الْمَكْتَبَةِ الْيَوْمَ.
lā kutuba fī hādhihi l-maktabati l-yawma
There are no books in this bookshop today.
A plural: the same accusative without tanwīn (compare the ordinary كُتُبٌ with tanwīn).
لَا طَالِبَ عِلْمٍ يُضِيعُ وَقْتَهُ.
lā ṭāliba ʿilmin yuḍīʿu waqtahu
No seeker of knowledge wastes his time.
طَالِبَ is muḍāf, so it has an ordinary accusative ending.
لَا أَحَدَ فِي الْمَسْجِدِ بَعْدَ الظُّهْرِ.
lā aḥada fi l-masjidi baʿda ẓ-ẓuhri
There is nobody in the mosque after noon.