Cannot, Can Not or Can't—Which Should I Use?
https://www.grammarly.com/blog/cannot-or-can-not/
Here is a quick summary: Can’t is a contraction of cannot, and it’s best suited for informal writing. In formal writing and where contractions are frowned upon, use cannot. It is possible to write can not, but you generally find it only as part of some other construction, such as “not only . . . but also.” Examples
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