1. “Finite Graphs and Networks.”;Busacker,1965
2. On the analytical forms called trees, with applications to the theory of chemical combinations;Cayley;Rep. Brit. Assoc. Advan. Sci.,1875
3. A note on plane trees;de Bruijn;J. Combinatorial Theory,1967
4. The number of homeomorphically irreducible trees and other species;Harary;Acta Math.,1959
5. The number of plane trees;Harary;Nederl. Akad. Wetensch. Proc. Ser. A,1964