. 2021 Jan 16;9(2):502–508. doi: 10.12998/wjcc.v9.i2.502
©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.
This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/Licenses/by-nc/4.0/
Figure 3.
First operation.