A feature where Soulver notifies in some way (May be by changing variable colour) to the user that variable is previously declared and this declaration will overwrite the previous one.

Justification : In a long code or a sheet there are situations when you unknowingly use the same variable twice or more than that which disrupts the desired calculations. It is even more difficult to find that error in a sheet if results are offset due to declaring the same variable twice. A subtle notification like that will avoid such mishaps.