  In this text I present some problems which led to the introduction of special
kinds of graphs as tools for studying singular points of algebraic surfaces. I
explain how such graphs were first described using words, and how several
classification problems made it necessary to draw them, leading to the
elaboration of a special kind of calculus with graphs. This non-technical paper
is intended to be readable both by mathematicians and philosophers or
historians of mathematics.

History and Overview;Algebraic Geometry;Geometric Topology