“…The complexity of simultaneous planarity for two graphs remains open, but it is tempting to conjecture that it is in P. In fact, we will state a (combinatorial) conjecture later which implies that simultaneous planarity is in P. Several special cases have been solved recently. One can test whether (G 1 , G 2 ) is simultaneously planar (i) in linear time if G 1 ∩G 2 is 2-connected (Haeupler, Jampani, Lubiw [22,23]), (ii) in linear time if G 1 ∩ G 2 consists of disjoint cycles (Bläsius, Rutter [9]), (iii) in quadratic time if a fixed embedding of each connected component of G 1 ∩ G 2 is given (Bläsius, Rutter [9]), (iv) in quadratic time if G 1 and G 2 are 2-connected, and G 1 ∩ G 2 is connected (Bläsius,Rutter [8]).…”