As always there is another point in arithmetic order. If we have an expression like 3ab + 2cd we do not mean to add 2 to the 3 * a * b first and only after that go and multiply our result by c and then by d. But I consider this a mathematics (lazy in notation and avoiding parenthesis)

REBOL languages require whitespace between terms, so the dense math convention is not suitable. Currently, 3ab and 2cd are invalid terms/numbers. But there's a proposal in REBOL to make this denote units. So this would be units ab and cd, and what they mean determines if they can be added.