The function swap_3 is used to swap the arguments
of a functor. The result is a functor f' that calls the original
functor f with the third and fourth argument exchanged, that is
f'(w,x,y,z,...)= f(w,x,z,y,...).
returns a functor equivalent to f, but
where the third and fourth argument are exchanged. Requirement: F is a model for
AdaptableFunctor with arity 4 ar 5.
ar