Which of the following phrases is correct or both are ok?

(1) "at least one of A and B"

(2) "at least one of A or B"

I first thought that (1) sounds more natural, but later found (2) on some websites.

They are different propositions, Mimi.

(1) "at least one of A and B" = one of both A and B, as a minimum, so 2 'things' as a minimum.

(2) "at least one of A or B" = either one A or one B, as a minimum, so 1 'thing' as a minimum.
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Dear Mister Micawber,

I appreciate your help again!!

I don't agree with Mister Micawber.

At least one "A and B" would mean one or more "A and B" as he writes.
But at least one OF A and B means A alone, or B alone, or both.
A lot of Anons don't agree with me. Fortunately, they don't carry much weight.
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Historically, "or" was considered ambiguous, so the language "one of A and B" was used as a substitute for just "A or B", not for "one of A or B". The law seems to have shifted, at least as far as the USPTO is concerned, so that "or" is now acceptable and "one of A and B" is now disfavored. I wonder if the courts agree with the USPTO?

At least one of A or B means "either A or B or both".

At least one of A and B means exactly the same.

However, the former is more natural (to me, a native English speaker, with more than 40 years of experience, and with brilliant English). The former should be used. A google search confirms it is the more common version.