Geodesic
Density and fractal property of the class of oriented trees
Jan Hubička1 ; Jaroslav Nešetřil2 ; Pablo Oviedo3 ; Jan Hubička ; Jaroslav Nešetřil ; Pablo Oviedo
1Department of Applied Mathematics (KAM), Charles University, Praha, Czech Republic
2Computer Science Institute of Charles University (IUUK), Charles University, Praha, Czech Republic
3Departament de Matemàtiques, Universitat Politècnica de Catalunya, Barcelona, Spain
Acta mathematica Universitatis Comenianae, Tome 88 (2019) no. 3, pp. 813-818 
Jan Hubička; Jaroslav Nešetřil; Pablo Oviedo; Jan Hubička; Jaroslav Nešetřil; Pablo Oviedo. Density and fractal property of the class of oriented trees. Acta mathematica Universitatis Comenianae, Tome 88 (2019) no. 3, pp. 813-818. http://geodesic.mathdoc.fr/item/AMUC_2019_88_3_a70/
@article{AMUC_2019_88_3_a70,
     author = {Jan Hubi\v{c}ka and Jaroslav Ne\v{s}et\v{r}il and Pablo Oviedo and Jan Hubi\v{c}ka and Jaroslav Ne\v{s}et\v{r}il and Pablo Oviedo},
     title = { Density and fractal property of the class of oriented trees},
     journal = {Acta mathematica Universitatis Comenianae},
     pages = {813--818},
     year = {2019},
     volume = {88},
     number = {3},
     url = {http://geodesic.mathdoc.fr/item/AMUC_2019_88_3_a70/}
}
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Voir la notice de l'article provenant de la source Comenius University

We show a density theorem for the class of finite proper trees ordered by the homomorphism order, where a proper tree is an oriented tree which is not homomorphic to a path. We also show that every interval of proper trees, in addition to being dense, is in fact universal. We end by considering the fractal property in the class of all finite digraphs. This complements the characterization of finite dualities of finite digraphs.