  In this work I investigate the statistical properties of a huge catalog of
closely interacting pairs of dark matter haloes, extracted from the Millennium
Simulation database. Only haloes that reach a minimum mass greater than 8.6
\times 10^10 Msun/h (corresponding to 100 particles) are considered. Close
pairs are selected if they come within a critical distance dcrit. I explore the
effects of replacing dcrit = 1 Mpc/h with 200 kpc/h on the evolution of
separations, lifetimes, total masses and mass ratios of these pairs.
