anchor.diff:             (multiple-value-bind (existing-sym presentp)
                  (find-symbol (symbol-name sym) *package*)
                (and presentp (eq existing-sym sym)))))
  -    (let* ((syms (sort (apropos-list regexp packages)
  +    (let* ((syms (sort (apropos-list regexp (when packages (ensure-list packages)))
                          (lambda (a b)
                            (let ((pa (package-name (symbol-package a)))
                                  (pb (package-name (symbol-package b))))
  
positive.code: the bad thing is that it's a PPCRE regexp. :-(
  "
    (let ((packages (if packages
                        (mapcar (function find-package) packages)
                        (list-all-packages)))
          (symbols  '())
          (compre   (create-scanner regexp :case-insensitive-mode t)))
  
negative.code: (defpackage "COM.INFORMATIMAGO.TOOLS.SYMBOL"
    (:use "COMMON-LISP"
          "CL-PPCRE"
          "COM.INFORMATIMAGO.COMMON-LISP.CESARUM.PACKAGE"
          "COM.INFORMATIMAGO.COMMON-LISP.CESARUM.LIST")
    (:shadow "APROPOS" "APROPOS-LIST")
    (:export "CHECK-DUPLICATE-SYMBOLS"
             "DUPLICATE-SYMBOLS"
  