In this task, you will be given a sentence, and you need to identify the set of coreference words. Coreferences are generally a set of words in the text that refer to the same person or thing. Your output set of coreference words must be strictly present in the given input sentence. Do not use any outside knowledge to create the set of coreference words. If there is a 'the' article before the person or thing you should include 'the' as well. Please separate the coreference words by commas in the output.

The chief returned a book to the librarian but he had damaged the book .
The, chief, he

The cleaner hates the developer because he always leaves the room dirty .
the, developer, he

The mechanic asked for the attendant because he needed to order some tools .

The, mechanic, he