Minus signs are ambiguous

The minus sign has two common usages:

This is a reasonable distinction on its own, but causes problems when expressions involve multiple values and operations. This makes things harder to learn, harder to teach, harder to program into a computer, etc.

For example, it’s common to write multiplication by putting values side-by-side, e.g. 2xtimes2x to mean “22 times xx”. Using the minus sign for two different operations makes this ambiguous, since 2x 2x could mean “two times negative xxor it could mean “two take away xx”; these are two very different things! Convention is to always treat such minus signs as subtraction, and use parentheses if we want multiplication, e.g. 2 ( -x )

Avoid unary minus: prefer over-bars for negatives

Compared to minus signs, “over-bar” notation seems to be more elegant for indicating negatives/opposites/inverses. It also extends naturally to the idea of negative digits.

Avoid binary minus: add negatives instead of subtracting

Addition is more “well behaved” than subtraction (it is commutative, associative, etc.), so it’s generally better to add negatives instead of subtracting.