The Free On-line Dictionary of Computing (30 December 2018):

user interface copyright

   There have been several attempts, mostly by big US software
   companies, to enforce patents and copyright on user
   interfaces.  Such legal action aims to restrict the use of
   certain command languages or graphical user interfaces to
   products from one software supplier.  This is undesirable
   because it either forces users to buy software from the
   company whose interface they have learned or to learn more
   than one interface.  An analogy is often drawn with the user
   interface of a car - the arrangement of pedals and steering
   wheel etc.  If each car manufacturer was forced to use a
   different interface this would be very bad for car users.

   Following a non-jury trial, which began in early January 1987,
   a federal judge ruled on 1990-06-28 that keyboard commands and
   on-screen images produced by Lotus Development Corporation's
   popular 1-2-3 spreadsheet are protected by copyright.
   Paperback Software International and subcontractor
   Stephenson Software Ltd. who lost the case, argued that the
   copyright applies only to the inner workings of the software.
   US District Judge Robert Keeton wrote that "The user interface
   of 1-2-3 is its most unique element and is the aspect that has
   made 1-2-3 so popular.  That defendants went to such trouble
   to copy that element is a testament to its substantiality".
   Defence attorneys had argued that the Lotus commands
   represented "instructions for a machine rather than the
   expression of an idea".

   Soon after this decision, on 1990-07-02, Lotus sued Borland
   International and the Santa Cruz Operation for producing
   spreadsheets (Quattro, Quattro Pro and SCO Professional)
   whose interfaces could be configured to look like 1-2-3's.

   (1994-11-16)