Function cut::lift_sum

pub fn lift_sum<'a, Row, F1, F2, Lift>(
    lift: Lift, 
    sum: AppSum<'a, Row, F1>
) -> AppSum<'a, Row, F2> where
    Row: 'a + SumFunctor,
    F1: 'a + TyCon,
    F2: 'a + TyCon,
    Lift: 'a + NaturalTransformation<'a, F1, F2>,