2. in : |R|
IdLnk
3. out : |R|
IdLnk
4.
i:|R|.
4. R(source(in(i))) & R(destination(out(i)))
4. & source(out(i)) = i
4. & & destination(in(i)) = i
4. & & in(destination(out(i))) = out(i)
4. & & out(source(in(i))) = in(i)
5.
i,j:|R|. 
k:
. 
x.destination(out(x))^k(i) = j
6. i : |R|
7. k :
8.
x.destination(out(x))^k(i) = i
(x.destination(out(x))) 
|R||R|
