Question: double negative

Why can't I do double negatives and why is it so difficult to do simple mathematics with negatives?


(a - b)


want to simply rewrite this by substitution for a simple quick calculation, repalce a and b with their values, e.g.,


-3 - -5


Maple complains!



maple complains!


This makes it impossible to not have to rewrite simple expressions just to get maple to work.


Surely there is a untary negative sign that I can use that will please maple?



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