  In this work we study preference systems natural for the Peer-to-Peer
paradigm. Most of them fall in three categories: global, symmetric and
complementary. All these systems share an acyclicity property. As a
consequence, they admit a stable (or Pareto efficient) configuration, where no
participant can collaborate with better partners than their current ones. We
analyze the representation of the such preference systems and show that any
acyclic system can be represented with a symmetric mark matrix. This gives a
method to merge acyclic preference systems and retain the acyclicity. We also
consider such properties of the corresponding collaboration graph, as
clustering coefficient and diameter. In particular, studying the example of
preferences based on real latency measurements, we observe that its stable
configuration is a small-world graph.
