They are the sort of friends who are so close that they trust each other with their lives.If one falls，the other is there to catch him. They are Wellman，whose legs were permanently injured nine years ago in a rock climbing accident，and Corbett，an experienced rock climber.Together，they climbed up Half Dome，the famous 2,000-foot rock in the Yosemite National Park，through one of the most difficult routes. During the climb，Corbett took the lead，hit in the metal spikes(尖状物) that guided the ropes and climbed up.Then，after Wellman pulled himself up the rope，Corbett went down to remove the spikes and climbed up again.This process was repeated time and time again，inch by inch，for 13 days.

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