Scaling and Inverse Scaling in Anisotropic Bootstrap percolation
  In bootstrap percolation it is known that the critical percolation threshold tends to converge slowly to zero with increasing system size, or, inversely, the critical size diverges fast when the percolation probability goes to zero. To obtain higher-order terms (that is, sharp and sharper thresholds) for the percolation threshold in general is a hard question. In the case of two-dimensional anisotropic models, sometimes correction terms can be obtained from inversion in a relatively simple manner. 
Aernout C.D. van Enter
math-ph cond-mat.stat-mech math.MP math.PR