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# internalVertices -- list the internal vertices of a tree

- Usage:
    `internalVertices T`
- Inputs:
  - T, an instance of the type LeafTree,
- Outputs:
  - a list, the internal vertices of T

## Description

An internal vertex of a tree is a vertex that is not a leaf, meaning it has degree at least 2. This function lists such vertices. Each vertex is specified by the partition of the set of leaves formed by removing the vertex. Each partition is given as a list of sets.

    i1 : T = leafTree(4,{{0,1}});

    i2 : internalVertices T

    o2 = {set {set {3}, set {2}, set {0, 1}}, set {set {1}, set {2, 3}, set {0}}}

    o2 : List

    i3 : #(internalVertices T)

    o3 = 2

## See also

- vertices(LeafTree) -- list the vertices of a tree

## Ways to use internalVertices:

- `internalVertices(LeafTree)`

## For the programmer

The object internalVertices is a method function.

The source of this document is in /build/macaulay2-88fgJW/macaulay2-1.25.11+ds/M2/Macaulay2/packages/PhylogeneticTrees.m2:1819:0.