Overmerging in N-body simulations
  The aim of this paper is to clarify the notion and cause of overmerging in N-body simulations, and to present analytical estimates for its timescale. Overmerging is the disruption of subhaloes within embedding haloes due to {\it numerical} problems connected with the discreteness of N-body dynamics. It is shown that the process responsible for overmerging is particle-subhalo two-body heating. Various solutions to the overmerging problem are discussed 
Eelco van Kampen