ALGO(G,A,B)
Z=NIL
INIT(G)
GT=TRASPOSTO(G)
for each b in B do
	c1[b]=nero

for each a in A do
	if(c1[a]=bianco)then
		dfs_visit(GT,a,c1)

for each a in A do
	c2[a]=nero

for each b in B do
	if(c2[b]=bianco)then
		dfs_visit(GT,b,c2)

if(c1[v]=nero && c2[v]=nero)then
	Z = Z u {v}

return Z