Function eschers::picture::quartet

pub fn quartet<P, Q, R, S>(
    nw: Rc<P>, 
    ne: Rc<Q>, 
    sw: Rc<R>, 
    se: Rc<S>
) -> Rc<impl Fn(&Bx) -> Rendering> where
    P: Fn(&Bx) -> Rendering,
    Q: Fn(&Bx) -> Rendering,
    R: Fn(&Bx) -> Rendering,
    S: Fn(&Bx) -> Rendering, 

Create a quartet of pictures