What exposition is provided by Huck which he claims the prequel to this story?

You are referring to Mark Twain's novel *The Adventures of Huckleberry Finn*. There is no official prequel to the story within the book. However, Huck does provide some exposition about his past and his relationship with Pap, which could be considered a form of prequel information.

Here are some examples:

* Huck's childhood with Pap: He describes the harsh and abusive treatment he received from his father, highlighting the escape that led him to live with the Widow Douglas. This provides insight into his rebellious nature and aversion to authority.

* His early life with the Widow Douglas: Huck recounts his interactions with the Widow and Miss Watson, showcasing his initial attempts at learning civilized manners and morality. This contrast with his background with Pap further emphasizes his internal conflict.

* His escape from Pap and the beginning of his journey: Huck explains his escape from his father's clutches, which sets the stage for his adventures with Jim and his journey of self-discovery.

While not a formal prequel, these narratives provide backstory and context that are crucial to understanding Huck's character and motivations.

If you are interested in learning more about Huck's past, there are several unofficial prequels written by other authors, but these are not considered canonical to Twain's work.