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Wald1
Notes for wikipage
Cox, Steven M. and Kris Fulsaas, ed., ed (2003-09). Mountaineering: The Freedom of the Hills (7 ed.). Seattle: The Mountaineers. ISBN 0898868289.
http://climbing.about.com/od/cliimbingtechniques/a/3RockFaces.htm
http://www.climbing.com/print/techtips/tech_tip_-_technique_-_heels_of_steel/
http://www.spadout.com/a/the-climbing-shoe-quiver-part-ii-slab/