COWSEL (COntrolled Working SpacE Language) is a programming language designed between 1964 and 1966 by Robin Popplestone. It was based on an RPN form of Lisp combined with some ideas from CPL. COWSEL was initially implemented on a Ferranti Pegasus computer at the University of Leeds and on a at the Bradford Institute of Technology; later, Rod Burstall implemented it on an Elliot 4120 at the University of Edinburgh. COWSEL was renamed POP-1 during the summer of 1966 and development continued under that name from then on.