2 | 8. ls: ||tr||. is-send(E)(tr[ls]) & ( j: ||tr||. ls < j  is-send(E)(tr[j])) Q:( ||tr|| Prop).
( i: ||tr||. Dec(Q(i)))
& ( i: ||tr||. Q(i))
& ( i: ||tr||. Q(i)  is-send(E)(tr[i]))
& ( i,j: ||tr||. Q(i)  Q(j)  tag(E)(tr[i]) = tag(E)(tr[j]))
& ( i,j: ||tr||. Q(i)  i j  C(Q)(j)) |