The GUI was first developed at Xerox PARC by Alan Kay, Larry Tesler, Dan Ingalls, David Smith, Clarence Ellis and a number of other researchers. It used windows, icons, and menus (including the first fixed drop-down menu) to support commands such as opening files, deleting files, moving files, etc. In 1974, work began at PARC on Gypsy, the first bitmap What-You-See-Is-What-You-Get (WYSIWYG) cut & paste editor. In 1975, Xerox engineers demonstrated a Graphical User Interface "including icons and the first use of pop-up menus".