Logically answering an informally posed question Let the following situation be the truth: "Each person has a unique passport number and every passport number is assigned to a person". Then consider the following statement: "Each passport number belongs to at most one person." Is the following statement TRUE or FALSE? * * * I'm unsure what to answer about this, because I could answer as follows: * FALSE, because implicitly it says that each passport number belongs to 0 (no person) or at most 1 person. And 0 (no person) would be false. * TRUE, yes, because it's correct that the number of owners for a passport number is less than or equal to 1. * * * Exactly this question arised in a test of mine. The master solution says TRUE. But I'm convinced that both answers have their justification. Do you think that the question is ill-posed or do you think that with formal reasoning one can convince himself about some solution?

If I take the numbers $2,4,6,$ and $8$, and I claim "Everyone one of these numbers is either even or odd", I am making a true claim, even if none of them are odd.

Same logic as with these passport numbers: If every passport number is assigned to exactly $1$ person, the claim that every number is assigned to either $0$ or $1$ person is still true.