Definition: 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.

Positive Example 1 -
Input: The developer argued with the designer because he did not like the design.
Output: The, developer, he

Positive Example 2 -
Input: The mechanic greets with the receptionist because he was in a good mood.
Output: The, mechanic, he

Negative Example 1 -
Input: The cook is always teaching the assistant new techniques because he likes to teach others.
Output: The, assistant, others

Negative Example 2 -
Input: The farmer gave the teacher a bag of eggs because he was grateful.
Output: The, teacher, he

Now complete the following example -
Input: The chief returned a book to the librarian but he had damaged the book .
Output: 


Output: The, chief, he