Overlapping Instantons
  Overlapping instantons have an action density profile that significantly deviates from the simple addition of the density profiles of single instantons. This turns out to have important consequences for identifying the proper instanton content of a given configuration. Most dramatic is the case where the instantons are parallel in group space, leading to the effect of hiding large instantons. Sufficiently large instantons can have important contributions to a confining interaction. 
M. Garcia Perez, T.G. Kovacs and P. van Baal