2015-03-25 22:38:09 +0100 commented answer Testing planarity on embedding gives wrong result Ah, I see, thanks. So, do you have any idea how much I can trust this this function (the version before you made it right)? I'm trying to Boyer-Myrvold in C++ and I wanted to use Sage for checking output of my program. 2015-03-24 13:57:56 +0100 commented answer Testing planarity on embedding gives wrong result Thanks! This was the second time I used Sage for planarity testing, so I thought it was rather my mistake. By the way, why were the computations run on cached embedding, instead of mine? (I did't get from the report) 2015-03-24 13:38:51 +0100 received badge ● Scholar (source) 2015-03-24 12:19:41 +0100 asked a question Testing planarity on embedding gives wrong result Hi, i've got planar embedding of K_4 which is not planar, but when I test it with is_planar(on_embeding=emb), it says that it is planar. Code: g = graphs.CompleteGraph(4) g.is_planar(set_embedding=True) True emb = {0 : [2,3,1], 1: [2,3,0], 2: [1,3,0], 3:[0,1,2]} g.is_planar(on_embedding=emb) True  So, what am I doing wrong?