I think it might be fair to say that Christian Queinnec's "Reasonable Lisp" had some influence on the ISLISP committee, but overall ISLISP as a language is very obviously intended to be "compatible" with Common Lisp, in the sense that an implementation could be conformant to both ISLISP and Common Lisp in a single "mode". In fact, Kent Pitman wrote an ISLISP "compatibility package" in Common Lisp in order to make sure it was do-able prior to the ratification of ISLISP. I.e., ISLISP can be implemented as a library for Common Lisp, without the need for a separate interpreter/translator.