Related uses of the relative and subjunctive

After est / sunt

To mark a characteristic, after another noun / pronoun etc.

This can work:

1. as a statement with a pronoun:
   is est qui librum scribet
   he is the sort of man who would write a book
2. as a statement with a noun:
   Cicero est qui librum scribet
   Cicero is the sort of man who would write a book
3. -as a negative statement:
   nemo est qui librum scribet
   There is nobody who would / will write a book
4. as a question:
   quis est qui librum scribet?
   Who is there who would write a book?
5. with a precise antecedent adjective:
   solus est qui librum scribet
   He alone is the kind of man who would write a book

As a simple replacement