Problem Statement

The task is to check that the terminal supports Unicode output, before outputting a Unicode character. If the terminal supports Unicode, then the terminal should output a Unicode delta (U+25b3). If the terminal does not support Unicode, then an appropriate error should be raised. Note that it is permissible to use system configuration data to determine terminal capabilities if the system provides such a facility.

Let's start with the solution:

(if (sub? "UTF-8" (or (sys "LC_ALL") (sys "LC_CTYPE") (sys "LANG")))
   (prinl (char (hex "25b3")))
   (quit "UTF-8 capable terminal required") )