Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
What is the difference between してはいない and していない?
NOTE: This post is inspired by this one, which touched upon this topic (though I never felt like a definitive or clear answer was provided).
"は" in this case is to restrict the extent. By restriction, you hint at something else beyond restriction such as:
If you say 後悔していない, 忘れていない or 言っていない, you just mean it.