Here's the email chain between RMS and Bruno Haible, author of CLISP: https://sourceforge.net/p/clisp/clisp/ci/tip/tree/doc/Why-CLISP-is-under-GPL Apparen

Here's the email chain between RMS and Bruno Haible, author of CLISP: https://sourceforge.net/p/clisp/clisp/ci/tip/tree/doc/Why-CLISP-is-under-GPL Apparently the situation was that CLISP was distributed as `lisp.a` and `libreadline.a` (with source for Readline included) and the end-user linked them together. Haible offered to write a `libnoreadline.a` library, exporting Readline's function but not providing their functionality, but RMS insisted that the result would still be a derived work of Readline.