Lotus 1-2-3 is a spreadsheet program that enables users to perform accounting functions electronically on a computer. Users manipulate and control the program via a series of menu commands, such as 'Copy,' 'Print,' and 'Quit.' Users choose commands either by highlighting them on the screen or by typing their first letter. In all, Lotus 1-2-3 has 469 commands arranged into more than 50 menus and submenus. Lotus 1-2-3 also allows users to write 'macros' to designate a series of command choices with a single macro keystroke. Once a macro is enabled it will perform the designated series of commands automatically. D released its first Quattro program to the public in 1987.D's objective was to develop a spreadsheet program far superior to existing programs, including Lotus 1-2-3. P sued D for copyright infringement. The district court found that D included in its Quattro and Quattro Pro version 1.0 programs 'a virtually identical copy of the entire 1-2-3 menu tree.' D did not copy any of P's underlying computer code; it copied only the words and structure of the menu command hierarchy. D did this to make them compatible with Lotus 1-2-3 so that spreadsheet users who were already familiar with Lotus 1-2-3 would be able to switch to D's programs without having to learn new commands or rewrite their macros. D achieved compatibility with Lotus 1-2-3 by offering its users an alternate user interface, the 'Lotus Emulation Interface.' By activating the Emulation Interface, users would see D menu commands on their screens and could interact with Quattro or Quattro Pro as if using Lotus 1-2-3, albeit with a slightly different-looking screen and with many D options not available on Lotus 1-2-3. A district court held that the Lotus 1-2-3 'menu structure, taken as a whole -- including the choice of command terms [and] the structure and order of those terms,' was protected expression covered by Lotus's copyrights. P sued D for copyright infringement. P and D filed cross-motions for summary judgment and eventually, the district court ruled that the D menu command hierarchy was copyrightable expression because a very satisfactory spreadsheet menu tree can be constructed using different commands and a different command structure from those of Lotus 1-2-3. The district court stated that 'the 'Quit' command could be named 'Exit' without any other modifications,' and that 'the 'Copy' command could be called 'Clone,' 'Ditto,' 'Duplicate,' 'Imitate,' 'Mimic,' 'Replicate,' and 'Reproduce,' among others.' Because so many variations were possible, the district court concluded that P's choice and arrangement of command terms, reflected in the Lotus menu command hierarchy, constituted copyrightable expression. D eventually appealed. D contends that the P menu command hierarchy is not copyrightable because it is a system, method of operation, process, or procedure foreclosed from protection by 17 U.S.C. § 102(b).