1 | 11. filter( e. is-send(E)(e) loc(E)(e) = x1;x)
swap adjacent[ loc(E)(x) = loc(E)(y)
& is-send(E)(x) & is-send(E)(y)
is-send(E)(x) & is-send(E)(y)] filter( e. is-send(E)(e) loc(E)(e) = x1;y) filter( e. is-send(E)(e) loc(E)(e) = x1;y) = filter( e. is-send(E)(e) loc(E)(e) = x1;x) |