4.3 Planar Graphs - possible trivial case

[SerDigby]

Hi, sorry another trivial case I thought perhaps worth checking.

We end up using gf ≤ 2_e_ to assess whether or not any given graph is planar, with g being the girth.
Acyclic graphs are considered to have infinite girth. It seems a graph like a tree or a single vertex would be considered planar but not satisfy the proof?

Thanks,
Enjoying the book!