Are identifiers of the form a#b permitted?
Yes: Racket, MIT, Gambit, Chicken, Scheme48/scsh, Guile, SISC, SCM, JScheme, STklos, Shoe, MiniScheme, TinyScheme, S7, SIOD, BDC, XLisp, Elk, Llava, Sizzle, FemtoLisp, Dfsch, Inlab, Sagittarius, Picrin, Chibi, Peroxide
No: Gauche, Bigloo, Kawa, Chez, Vicare, Larceny, Ypsilon, Mosh, IronScheme, NexJ, KSi, SigScheme, Scheme 9, RScheme, Unlikely, Rep, Schemik, SXM, Foment, Owl Lisp