Well, then the statement 'functions many only recurse up to some limit' applies to Common Lisp as specified but not to this implementation of it. This isn't par

Well, then the statement 'functions many only recurse up to some limit' applies to Common Lisp as specified but not to this implementation of it. This isn't particularly unusual, since language implementations often have capabilities which aren't part of the specifications (see the many extensions to C, for example. e.g. in standard C you can't assume that type punning using a union will be defined, but almost all implementations explicitly allow for it). These are differences in the semantics of the language (namely in what is and isn't allowed), not just optimisations.