Symbols in COMMON-LISP are all in upper case. (Yes, I know, it's a little known fact about COMMON-LISP). So why can't we look up them in upper case? Let's ignore case when completing symbols in slime-hyperspec-lookup and everybody will be happy.
(defun slime-hyperspec-lookup (symbol-name) "A wrapper for `hyperspec-lookup'" (interactive (list (let ((completion-ignore-case t) ;; <<<<--------- (symbol-at-point (slime-symbol-name-at-point))) (if (and symbol-at-point (intern-soft (downcase symbol-at-point) common-lisp-hyperspec-symbols)) symbol-at-point (completing-read "Look up symbol in Common Lisp HyperSpec: " common-lisp-hyperspec-symbols #'boundp t symbol-at-point 'common-lisp-hyperspec-history))))) (hyperspec-lookup symbol-name))