Function compose_semifinite 

pub fn compose_semifinite<K: ArrayKind, T>(
    lhs: &FiniteFunction<K>,
    rhs: &SemifiniteFunction<K, T>,
) -> Option<SemifiniteFunction<K, T>>
where
    K::Type<T>: Array<K, T>,

As a special case, a we can precompose a FiniteFunction with a SemifiniteFunction. This is also overloaded with the >> syntax.