Function bind_mapped2 

pub fn bind_mapped2<S1: Clone + PartialEq + 'static, S2: Clone + PartialEq + 'static, T: 'static>(
    s1: &Observable<S1>,
    s2: &Observable<S2>,
    map: impl Fn(&S1, &S2) -> T + 'static,
) -> Binding<T>

Create a binding from two observables combined by map.