[eclipse-users] elements/3 with a list of variables

I have two lists of variables, Xm and Xn and want to implement the
following constraints, where each variable in Xm represents an index of Xn
and vice versa.

forall n Xm[Xn[n]] = n
forall n Xn[Xm[n]] = n

However, I cannot do this using element/3 because it requires that the
list does not contain any variables.

I hope that someone has some suggestions as to how to solve this.

Regards,

Brammert