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:

10 REM There is no Unicode delta in ROM
20 REM So we first define a custom character
30 FOR l=0 TO 7
40 READ n
50 POKE USR "d"+l,n
60 NEXT l
70 REM our custom character is a user defined d
80 PRINT CHR$(147): REM this outputs our delta
9500 REM data for our custom delta
9510 DATA 0,0,8,20,34,65,127,0