At:
list-list-connect transitivity
For any graph
A,B,C:V List. A-- > *B B-- > *C A-- > *C
By:
Unfold `list-list-connect` 0
THEN
Unfold `l_all` 0
THEN
Unfold `list-connect` 0
THEN
Unfold `l_exists` 0
THEN
InstHyp [x] 6
THEN
ExRepD
THEN
InstHyp [y] 5
THEN
ExRepD
THEN
InstConcl [y@0]
THEN
Connect
Generated subgoals:
For any graph
A,B,C:V List. A-- > *B 
B-- > *C