In the academic field, it is very common to quote other people's research results and opinions, which is not only a respect for the original author's labor achievements, but also conducive to readers' understanding and evaluation of the value of the paper. Therefore, even if the papers have been published and included in the collection of papers, the source should be clearly indicated to ensure the compliance of academic norms.
If the paper is included in the collection of essays after publication, the source of publication should be indicated. This is because, even if the paper has been published and included in the collection of papers, the original source of publication should be indicated to show the source and background of the paper.