This article researches robots that explore unknown graphs and can place pebbles to distinguish nodes: "The Power of a Pebble: Exploring and Mapping Directed Gr

This article researches robots that explore unknown graphs and can place pebbles to distinguish nodes: "The Power of a Pebble: Exploring and Mapping Directed Graphs (1998)" by Michael A. Bender , Antonio Fernandez , Dana Ron , Amit Sahai , Salil Vadhan http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.2161 http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.2...