## Abstract

Two rooted locally finite trees are considered equivalent if both can be embedded into each other as topological minors by means of tree-order preserving mappings. By exploiting Nash-William's Theorem, Matthiesen provided a non-constructive proof of the uncountability of such equivalence classes, thus answering a question of van der Holst. As an open problem, Matthiesen asks for a constructive proof of this fact. The purpose of this paper is to provide one such construction; working solely within ZFC we illustrate a collection of ω_{1} many topological types of rooted trees. In particular, we also show that this construction strengthens that of Matthiesen in that it also applies to free (unrooted) trees of degree two.

Original language | English |
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Pages (from-to) | 794-795 |

Number of pages | 2 |

Journal | Discrete Applied Mathematics |

Volume | 340 |

Issue number | 4 |

DOIs | |

Publication status | Published - 1 Apr 2017 |

## Keywords

- Locally finite trees
- Topological minor
- Topological types
- Well-quasi-order

## ASJC Scopus subject areas

- Theoretical Computer Science
- Discrete Mathematics and Combinatorics