#![feature(slice_patterns)]

fn f<T>(_: &T, _: &T) -> T {
    unimplemented!();
}

use itertools::Itertools;

fn test<T>(vec: Vec<T>) -> Vec<Vec<T>>
where
    T: Clone,
{
    let n = vec.len();
    let mut vec: Vec<_> = vec.into_iter().combinations(n).collect();

    for (i, it) in vec.iter_mut().enumerate() {
        let (left, rigth) = it.split_at_mut(i);
        if let [y, rigth..] = &mut rigth[..] {
            for x in left.iter_mut().chain(rigth.iter_mut()) {
                *x = f(x, &y);
            }
        }
    }

    vec
}