Partially bent or folded under or back (like the corner edge on the cover of a book, the overhang on a metal roof after being bent by wind, etc.).
That metal roof is bent back because of the strong winds.
To bend or fold s.t. over (as when marking a page in a book, hemming a garment, etc.).
The -un imp. focuses more on folding or bending s.t. over in order to make room to do s.t. else. The -an imp. focuses more on affecting a part of s.t. by bending, folding or hemming.
That roof has become bent over by the wind.
Who folded the cover back/under on this book?