Key Points:

The word لَيْسَ

لَيْسَ - is not

لَيْسَ is used in nominal sentences

feminine form: لَيْسَتْ

In a sentence with لَيْسَ, the mubtada is called ismu laysa and the khabar is call khabaru laysa

Examples:

ليس الكتاب بجديدا → The book is not new

ليست زينب بمريضةٍ → Zaynab is not sick

Forms of لَيْسَ

Note: بِ is added to the khabar and makes it majrur. It is not added if the khabar is a prepositional clause.

Example:

لست من اليابان → I am not from Japan

In a sentence with a prepositional clause, the ismu laysa comes after the khabaru laysa*:

ليس لي اخوة → I have no brothers

أنَّ with prepositions

If أنَّ is in the sentence, the noun stays mansub, because it is ismu inna (usually nouns following prepositions are majrur)

Example:

أنَّ لي إخوتٌ

*this is the same as mentioned in book 1, where the mubtada comes after the khabar