most teachers want some "external sources" to deepen your understanding and "improve" the argument
If this is a requirement then it should be listed in the prompt.
Every paper I've had to do that required sources would specify a minimum number of sources, otherwise it's just "cite them correctly if you do use them"
moreover, they'll probably want him to cite the book
It's a play, not a book. But fair point
Tbh though the only correct answer is
Ask your teacher.
