ensure coerce only applies to multiplication

@ct-clearhaus OK, then what is "money" x "money"? :wink: The example is not appropriate. If it doesn't make sense, then we shouldn't allow the multiplication of `Money` (rhetorical question)?

I think you miss the whole point of coercion. It's perfectly acceptable, as used in everyday practice, to say that if one operand is numeric you can coerce it as the "base unit" and perform the operation.