We have already mentioned above that if the original document is not available, its photocopy is provided by a document delivery service. The introduction of the fast plain paper copiers (PPC), which was, pioneered by Xerox Corporation (the copying process is often called Xerography), has revolutionised the copying process. The demands for photocopies have also considerably increased. Libraries and information centres, therefore, have developed photocopying facilities to provide reprography service. The PPCs are not merely copying devices, but they can also produce multiple copies of documents. It should be noted that providing photocopies of documents is governed by the Copyright Laws, e.g., the U.K. permits taking one photocopy of a document provided that the requester signs a declaration stating that the copy is for "research or private study".