I found these example sentences in the book English Made Simple, Revised Edition: A Complete, Step-by-Step Guide to Better Language Skills
I am not quite sure the meanings of sentence 3 and sentence 4.
He had believed that he trisected angles.
He had believed that he had trisected angles.
Down below are my interpretations:
Sentence 3 means he once believed the fact that "he trisected angles" but manybe didn't believe it afterwards sometime in the past.
Sentence 4 means he believed the fact that he trisected angles, and these things all happened before something(something in the past.)
However, it raised my curiosity the differences between them(the past perfect tense in the noun clause affects the meaning at all?)
Down below are two examples sentences I created
He had stated that he talked to the girl.
He had stated that he had talked to the girl.
What is the difference? So would you all help me understand the concept of the sequence of tenses?