1 + 1 = 2
Is fairly unambiguous until you introduce operator overloading (and why i despise overloading).
It is only unambiguous if you specify the numbering system you are using ;)
</pedantic>
What is it specifying—or, perhaps a better question, what would an implementation look like? It might be more precise to say "I have yet to encounter an implemented spec that was not in some way ambiguous."