praveenRamalingam/khan-exercises — comment on commit a9bb40285ae86b05c8cb4e498a51ccd2fb330b06
File: utils/expressions.js line 459
By spicyj:

Actually, expr intentionally doesn't simplify A – (–B) to A + B but it does simplify A + (–B) to A – B, so the ensure should probably just be changed to add the negative instead of subtract. (There are exercises that rely on this behavior; we shouldn't change it.)