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Not obvious. Astronomers are actively looking for signatures of exomoons around exoplanets. So "sun plus moon" could mean that too.

The OP said moon + sun, rather than sun + moon. We have no idea yet if celestial math is non-communicative.

*commutative

Well, that too.

Well you find the signature by looking for a dip in but sun's luminosity. So minus might be the better relationship here