You may be right, maybe I've just only looked at Scheme lately and thought "?" had migrated to Common Lisp.
https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html seems to indicate that you could use ? in a common lisp function name, though.
https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html seems to indicate that you could use ? in a common lisp function name, though.