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a 2-CNF formula is satisfiable if and only if there is no variable that belongs to the same strongly connected component as its negation..
Look at this example:
Any variable and its negation belong to the same strongly connected component, but it's not possible to satisfy these formulas.
What I'm doing wrong?
PS: With 
formula, I want to force x = 1
If i remembered it correctly, for each a=>b you should also add -b=>-a edge
That was it. Thank you :)
We can derive two implications from (avb): ¬a->b, ¬b->a.