Hello. I wonder if there is a function like \x -> (x, x) in the standard libraries. I looked up in Hoogle. It gave me links: 1. https://hackage.haskell.org/package/utility-ht/docs/Data-Tuple-HT.html#v:dou... 2. https://hackage.haskell.org/package/extra/docs/Data-Tuple-Extra.html#v:dupe 3. https://hackage.haskell.org/package/relude/docs/Relude-Extra-Tuple.html#v:du... None of these is to the standard library. I wonder if there is an intentional omission for some important reason? If not, I think this function should be added to Data.Tuple. I know some of the persons that make decisions here like Category theory, so I point out this function is mentioned in Categories for the Working Mathematician, as δ, the diagonal function, on page 3 (second edition), although set with angular brackets. Have a great day.