{{arromdee}}: "A subset of the Odd Couple wherein the odd couple are identical twins. Usually brothers or sisters, with the exception of The Patty Duke Show"

From this I conclude that the Patty Duke Show features identical twins who are not brothers or sisters.

Someone familiar with the show, please fix this...

LooneyToons: No need to fix anything. ''ThePattyDukeShow'' was about a pair of identical ''cousins''; this was, in fact, written right into the theme song. (Later) Never mind, I see someone made the fix anyway.

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{{Fly}}: Cutting Les Enfants Terribles and moving them to SiblingYinYang.

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{{Micah}}: I just trimmed the Gordon R. Dickson example substantially.