Function grow 

pub fn grow<T, Q: GetBeginEnd<T>, R: GetBeginEnd<T>, S: GetBeginEnd<T>, C: CpCmp<T>, F: GetBeginEndOption<T, Q>>(
    x: &R,
    y: &S,
    t: &C,
    f: &F,
) -> Q

Given 2 instances of GetBeginEnd it returns a range that contains both.