I have to check whether a graph is planar. The given type is
$$ e ≤ 3v − 6 .$$
From Wikipedia:
Note that these theorems provide necessary conditions for planarity that are not sufficient conditions, and therefore can only be used to prove a graph is not planar, not that it is planar. If both theorem 1 and 2 fail, other methods may be used.
I am wondering what should I do to prove that a graph is planar.