Hello guys,

There is an infinite tree structure named *"the 3-1 tree"*, denoted by $T_{3-1}$. The tree is constructed as follows:

The origin vertex (which can be referred to as the zeroth level) has two sons. In each level $n$ we have $2^n$ vertices. In order to construct the next level, we split the $2^n$ vertices into two groups (the **left half** which consists of $2^{n-1}$ vertices and the **right half** which consists of the other $2^{n-1}$ vertices). From each **left** vertex we have three edges leaving it (therefore it has three sons) and for each **right** vertex we have only one edge leaving (therefore it has only one son). This way, in every level there are indeed $2^n$ vertices and a total of $2^{n+1}$ edges leaving that level. This is the structure.

It is a known fact that simple weighted random walk (all edges have weight 1, i.e. $c(x,y)=1$ $\forall$ $x,y\in T_{3-1}$) on $T_{3-1}$ is recurrent. I would like to prove this using simple tools such as electrical networks, martingales and standard probability tools.

Thank you very much!