Footwear with a sole portion for protecting the lower surface of a foot only and support means for slidably receiving the foot for securing the footwear thereto while leaving the toes, heel, and ankle entirely exposed is provided with a pocket on or in the support means opening outwardly to permit insertion...http://www.google.com.hk/patents/US4471539?utm_source=gb-gplus-share專利 US4471539 - Footwear having an auxiliary pocket
