How to prove you wrote it first

One may write a very good article and it may get copied on inteet, or slightly modified, rephrased etc... and after a while it is not even known who did it first. Now I know this is not likely so I ask more theoretically, just in case... Assume someone writes your content or slightly modified version, copyrights it, then after a while sees your article on your website and tells you that you stole his work. How do you prove you wrote it first? Or what steps do you take, if any, when each...

How to prove you wrote it first WordPress ...