fun trivial(x,y,z) = 1.0;



fun mouse(shrew) = shrew::nil;



fun easy(simple, complex) = simple orelse complex > 0;




fun trout(salmon, pike, mackerel, sole) =
    let
        val snapper = (salmon, 4);
        val eel = if hd(pike) then [mackerel, tl(pike)]
                  else [];
    in
        {scales = "a " ^ #1(snapper),
         tail = (eel, sole)}
    end;