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We study the percolation threshold for fully penetrable discs by measuring the average location of the frontier for a statistically inhomogeneous distribution of fully penetrable discs. We use two different algorithms to efficiently simulate the frontier, including the continuum analogue of an algorithm previously used for gradient percolation on a square lattice. We find that c = 0.676 339 0.000 004, thus providing an extra significant digit of accuracy to this constant.
Quintanilla et al. (Wed,) studied this question.