I am not a lawyer so I can't say with certainty, but judging by the exchange between Richard Stallman and Bruno Haible, the author of CLISP, it may well be requ

I am not a lawyer so I can't say with certainty, but judging by the exchange between Richard Stallman and Bruno Haible, the author of CLISP, it may well be required: https://sourceforge.net/p/clisp/clisp/ci/default/tree/doc/Why-CLISP-is-under-GPL https://sourceforge.net/p/clisp/clisp/ci/default/tree/doc/Wh...