Decorated trees

Abstract

We study a class of combinatorial objects that we call ``decorated trees''. These consist of vertices, arrows and edges, where each edge is decorated by two integers (one near each of its endpoints), each arrow is decorated by an integer, and the decorations are required to satisfy certain conditions. The class of decorated trees includes different types of trees used in algebraic geometry, such as the Eisenbud and Neumann diagrams for links of singularities and the Neumann diagrams for links at infinity of algebraic plane curves. By purely combinatorial means, we recover some formulas that were previously understood to be ``topological''. In this way, we extend the generality of those formulas and show that they are in fact ``combinatorial''.