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The probability R₋ (p) for a site percolation cluster to span a square lattice of side L at occupancy p is reexamined using extensive simulations and exact calculations. It is confirmed that R₋ (p₂) 1/2 as L in agreement with universality but not with renormalization-group theory. Many estimates of p₂ that derive from R₋ (p) are shown to scale with L more weakly than normal finite-size scaling, and the value p₂=0. 592 74600. 000 0005 is determined.
Robert M. Ziff (Mon,) studied this question.