The authors obtain a number of relations, including a dissymmetry theorem, for enumerating various types of 2-trees. For example, they give recurrence relations for the number of unlabelled rooted and unrooted 2-trees; and they determine the asymptotic behaviour of the number of unlabelled 2-trees and the number of oriented-edge rooted 2-trees.
Reviewer: J.W.Moon (Edmonton)