anchor: The fact, according to geologists, is that the Kathmandu Valley was indeed once a lake, though the valley's waters now drain through the narrow cleft of Chobar Gorge, which was most likely created by a large earthquake.)
positive: Geologists believe that the Kathmandu Valley was a lake at some point in its history.
negative: The fact, according to geologists, is that the Kathmandu Valley has never contained a significant amount of water.