James is in a room with three other people: Alice, Bob, and Spencer. Alice and Bob are married to each other, but James knows that Bob is secretly having an affair with Spencer.
James is going to announce the identity of his "baby," the person he loves the most in the whole world. He remarks, truthfully, about the occupants of the room: "Everybody loves my baby, but my baby doesn't love anybody but me."
Which person is James's baby?
To formalize definitions: we assume the love is a directional relationship P=>Q
where each endpoint P
and Q
represents some person in the room. We allow the possibility that a person may have any number of incoming and outgoing love relationships concurrently. (So, A
may love B
, but B
might not love A
back, and A
may love C
while still also loving B
as well.)
(I personally discovered this curiosity in The Cuckoo's Egg by Clifford Stoll, but it certainly predates that work, since the song "Everybody Loves My Baby" was written several decades prior, in 1924.)