$${\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{\,-\,}} = {\mathtt{2}}{\mathtt{\,\times\,}}\left(\underset{{\tiny{\text{Error: Unknown Identifier}}}}{{\mathtt{x}}}\right){\mathtt{\,-\,}}{\mathtt{\,\small\textbf+\,}}$$
.
) 