1 | 5. x: |E| 6. y: |E| 7. is-send(E)(x) 8. is-send(E)(y) 9. y =msg=(E) x 10. loc(E)(x) = loc(E)(y) 11. x1,y:|E|.
is-send(E)(x1) 
is-send(E)(y)  (y =msg=(E) x1)  loc(E)(x1) = loc(E)(y)  sublist(|E|;[x1; y]; < tr > _tag(E)(x)) 12. sublist(|E|;[x; y]; < tr > _tag(E)(x)) sublist(|E|;[x; y];tr) |