A process icon based on a tunnel concept in which the icon has an input and an output portal through which an object is dragged in order to invoke the process. The direction of the process invoked (e.g., encrypt to decrypt or decrypt to encrypt) can be denoted and determined by the portal through which...http://www.google.com.hk/patents/US5561758?utm_source=gb-gplus-share專利 US5561758 - Tunnel icon
