Image of a graph as mathematical structure. Showing all trees with 1, 2, 3, or 4 leaves.
Date
Source
Arthur Cayley (1859): On the Theory of Analytical Forms called Trees. Second Part. In: Philosophical Magazine, Vol. 17, p. 374-378. (Reprint in: The Collected Mathematical Papers of Arthur Cayley. Vol. 4, Cambridge University Press, Cambridge, 1891, p. 112-115; digital version at https://archive.org/details/collmathpapers04caylrich)