https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.rposition Description should provide a clear meaning for 'index' – index within the collection, or index as number of iteration? Examples for rposition should demonstrate a clear difference from position. Here's the example of rposition with an added comparison with the result of the situation with position. ``` let a = [1, 2, 3]; let mut iter_p = a.iter(); let mut iter_r = a.iter(); assert_eq!(iter_p.position(|&x| x == 2), iter_r.rposition(|&x| x == 2)); ``` My proposition: use the same example as position(F) ``` let a = [1, 2, 3, 4]; let mut iter = a.iter(); assert_eq!(iter.rposition(|&x| x >= 2), Some(3)); ```