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I have n sectors, enumerated 0 to n-1 counterclockwise. The boundaries between these sectors are infinite branches (n of them).

These branches meet at certain points (junctions). Each junction is adjacent to a subset of the sectors (at least 3 of them).

By specifying what sectors my junctions are adjacent to, I can completely recover the tree. This seems like something known, but I would like a reference to it.

The number of trees with n branches is given by http://www.oeis.org/A001003 and this is quite easy to prove.

Furthermore, if I order the sectors in the description of the junctions, I can make this representation unique.

Example: (0,1,2,3,4,5) represents the tree with only one vertex, and 6 branches connected to this junction.

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Perhaps it's just me, but I'm completely unable to parse this. Could you perhaps explain what you mean by sectors, infinite branches, junctions and what is the tree? A picture, perhaps? –  Alon Amit Feb 17 '10 at 1:11
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This is almost, but not quite, what a Prufer code does: en.wikipedia.org/wiki/Pr%C3%BCfer_sequence –  Qiaochu Yuan Feb 17 '10 at 3:20
    
I cannot post more hyperlinks since i am a new user, Here are 4 examples of such trees (ignore vertices with degree 2 or less) www2.math.su.se/~per/bloggimages/treeCombined22.png www2.math.su.se/~per/bloggimages/treeCombined12.png –  Per Alexandersson Feb 17 '10 at 16:51

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up vote 1 down vote accepted

I realized that taking the dual of my trees, I always get an n-gon, where some chords, the faces in the dual are my junctions. The bijection is now trivial.

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