In a MacOS Objective C project with Xcode 12.5.1, I tried to use max(). Received an error, and pressed "Fix" and I put #include math.h in a header. Subsequently, when I ran the project, I got two errors in a row saying "The document math.h cannot be saved...You don't have permission, etc." and when I press OK, I get the same message again. The instructions are open the file in the finder to change permissions. I don't have that file anywhere on my computer. So I deleted the include, removed the max() function and I still get the errors, although the project builds without other errors and the test app works.
I've searched the project for any reference to math.h and found none.
Now when I try to quit Xcode, I get an error that I don't have permission to write to the folder with math.h and choice is to Duplicate (what???) or OK. I choose OK and I cannot quit Xcode.
So, how do I remove whatever this is with math.h to get back before I ever tried using max()???