This question is from Kunen's set theory book.
My questions are:
What is the definition of isomorphism between forcing notions?
When do we say that two forcing notions $\mathbb{P},\mathbb{Q}$ are equivalent?
Are these two (i.e. Isomorphism and equivalence) between forcing notions same or there are equivalent forcing notions that are not isomorphic?
How to find out that two forcing notions are isomorphic?