the reference answer GPT ᴼ ᴾ ᴱ ᴺ ᴬ ᴵ < br / > this error is due to the \ standardtilde command has been defined, so can't define again. The solution is to delete or comment out the \standardtilde command you defined, or change the name of the command. Meanwhile, the \end command is a LaTeX reserved command and should not be used as the name of a custom command.
Check your LaTeX source for the existence of custom \standardtilde or \end commands and modify or delete them as described above.
