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http://mathcs.sn167.macalester.edu/groups/paralleledudev/weblog/1f229/pondless_waterfall.html http://cehsp01.d.umn.edu/groups/mary/weblog/83c8f/pondless_waterfall.html http://hopper.macalester.edu/groups/paralleledudev/weblog/a4b1c/pondless_waterfall.html http://discovery.unl.edu/groups/mert/wiki/80be7/pondless_waterfall.html http://wiki.fis.edu/groups/jenniferkoal/weblog/eada1/pondless_waterfall.html