P. D. Seymour studied square-lattice bond percolation with D. J. A. Welsh. Their work constructs crossing bounds for rectangles from square-crossing information, using positive correlation and geometric combinations of crossing events. Such scale comparisons are central to Russo-Seymour-Welsh theorem and planar critical connectivity.[ref]
Percolation probabilities on the square lattice by P. D. Seymour and D. J. A. Welsh. Introduction and Sections 4–5
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