I've looked at Is it acceptable to copy and paste questions from other sites? and A policy on plagiarism, and I'm aware that puzzles which are directly copy-pasted from other sites or sources without attribution are liable to be deleted for plagiarism. Likewise, it's clear that puzzles which are directly copy-pasted with attribution are not plagiarised, and won't be deleted for that reason.
My question is: what about puzzles which are paraphrased from other sites or sources?
Let's say I find a cool maths puzzle on a website somewhere which I want to share on Puzzling SE, but I rewrite the problem in my own words. Perhaps I make some sort of padding or story element around it, but when you boil it down to the essential mathematical content, it's the same idea as I found on another site. Do I need to link back to the place I found it, or can I just post it as if it was my own invention, since the presentation is my own work and the essential ideas of mathematical theorems and proofs are free and uncopyrightable?
Disclaimer: I have done this in the past, before I was aware of PSE's plagiarism policy: found maths or logic puzzles on the web and used the ideas to post my own rewritten versions here. But please don't go on a witch hunt and start flagging or deleting a bunch of my posts for plagiarism: if the answer to this question is "yes, you do need to provide attribution", then I'll happily go through my old questions one by one and edit in links where appropriate.