I was doing some exercises with must and have to.
I learnt that "have to" have to be used with laws or obligations, something you must do because of a external factor.
But in these exercises they use "must" to say a obligation about traffic signs, what I think must be "have to".
"You have to turn left." is replaced by "You must turn left."
Is this choice because many laws have the negation option?
So, by convention they use "must" to negation be implicit like "mustn't" and not "don't have" what may cause some misunderstoods.
Or this is because we suppose that sign is "speaking" with us?
Can I use "You have to turn left" instead of "You must turn left" ?