Wording about ownership rules; Rc enabling multiple ownership that isn't allowed

[LCamel]

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• I have searched open and closed issues and pull requests for duplicates, using these search terms:

  • is:issue There can only be one owner at a time.
  • is:issue "one owner"

• I have checked the latest main branch to see if this has already been fixed, in this file:

  • https://github.com/rust-lang/book/blob/71352deb20727b4dda9ebfe8182709d5bf17dfea/src/ch04-01-what-is-ownership.md?plain=1#L92

URL to the section(s) of the book with this problem:

• https://github.com/rust-lang/book/blob/71352deb20727b4dda9ebfe8182709d5bf17dfea/src/ch04-01-what-is-ownership.md?plain=1#L92
• https://github.com/rust-lang/book/blob/71352deb20727b4dda9ebfe8182709d5bf17dfea/src/ch15-04-rc.md?plain=1#L4

Description of the problem:

In Chapter 4, it says: "Ownership Rules ...... There can only be one owner at a time." In Chapter 15, it says: "However, there are cases when a single value might have multiple owners."

Is it still a rule?

Suggested fix: