off topic (but still graph theory)

I've heard of a case where a woman married her direct uncle.¹

Now I started wondering:

Is it legally possible that she is also his direct aunt?

I don't think so, but I can't wrap my head around it ...

(FWIW marrying your cousin counts as legal, like in most western* countries, the taboo stems from medieval Catholic church law)

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

*) surprisingly many US states don't fall under my western definition - > Cousin marriage

°) turns out laws are so inconsistent, that I need to define it:

German rules:

Spoiler Update

at least one of the pair can only be a half-uncle/aunt. Otherwise one parent on each side of the marriage become their own grandchild.

is it even still possible with half-siblings?

Updates

¹) since I've been asked: this was a Jewish marriage in Cairo/Egypt. In the Middle East marriages are mostly regulated by the communities, and apparently it's not a taboo in Judaism. Avunculate marriage lists another (again Jewish) case in New York, which was upheld in court.

As always you'll also find many examples in the pedigrees of royal houses, like the Windsors.

Replies are listed 'Best First'.
Re: Pairing Riddle (OT)
by LanX (Saint) on Apr 25, 2026 at 13:27 UTC
    Given the down votes it attracted, it might have been better to motivate it with breeding dogs to avoid touching on taboos.° =)

    But I enjoyed it from a mathematical perspective, since it's a a problem which can be perfectly described in graph theoretic terms: a directed graph with a "child of" relation with certain restrictions:

    • indicate the marriage with one child
    • max 2 arrows per node (to parents)
    • no cycles (no grandfather paradox)
    • no shortcut relation to chained connection (forefathers/-mothers are forbidden as parents)
    • always 4 different grandparents(i.e. 2nd degree connections) (sibling marriage is forbidden)

    Here the solution in short, but hidden behind a spoiler tag to protect those interested.

    • both full uncle/aunt relationship: is not possible without creating a "time paradox". Otherwise 2 members of the parents in-law generation become each others child. (Uncle: "My parents are your grandparents" and Nephew: "Your parents are my grandparents") That's violating the "no cycle" criteria.
    • one full and one half uncle/aunt: forbidden because at best (no cycle) one parent has to be remarried to his/her own grandchild.¹ Violating the "no shortcut" rule.
    • both half uncle/aunt: feasible - take 2 couples with children and remarry one of both couples with a child from the other couple. The offsprings are legal and become each others half uncle/aunt (like both can say your father is my grandfather or vice versa)

    I'll try to add a character graph later.

    Update

    Not easy to draw.

    Arrows go upwards meaning "child of". (Didn't indicate gender since it didn't really matter. Chose any of 4 combinations for B and X and adjust the partners accordingly :)

      

A   B   X   Y
 \ / . , \ /
  C   .   Z
   \ ’ . /
   🤵🏻‍♂️   👰🏻‍♂️
     \ /
     👶🏻

    Hope it's clear why the bride is C's half-sister by B, and the groom is Z's half-brother by X. And all above rules are respected.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    see Wikisyntax for the Monastery

    °) apparently do most so called "purebred" dogs have an inbreeding factor of 25%. That's like the outcome of incest. One more reason why I'd always opt for a mongrel.

    ¹) in some western countries this is technically legal, because the laws don't cover that case.

[reply]
      Hi LanX, there is another possibility not mentioned in your spoiler:

      To be the niece and the aunt of "Uncle" at the same time, the woman needs to be child of his brother and his grandfather.

      • => the mother of the woman has married both of them (not at the same time, of course!)
      • => in order to prevent any bloodline-issues, the biological father of the woman is someone completely different and the mother of the woman had no children neither with the brother nor with the grandfather

      seems to be much easier than originally thought ... but does not involve any graph-theory ...

      So long, Rata

[reply]

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