User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-4649443-20121111201446/@comment-4531192-20121119153628

What you stated above is mathematically incorrect, as if A = B, then B = A.

Another way to look at this question is by taking a human example: Say a man whom we'll call Bob was born in Greece, but moved to Italy shortly after having turned 18. He lives in Italy long enough to get citizenship, and then moves back to Greece. He then marries a Greek woman (say her name is Marie) and the two have a kid (Mark). Mark will be Greek even though his father Bob has double nationality. However, Mark will not be Italian, unlike his father, who is both Greek and Italian. The same logic can be used here as the gods have a double nationality type of deal, but their children are only of one "nationality" (Greek or Roman).