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Add some debugging information
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Do not patch split environment as it does more harm than good (and test it)
Make label information global to fix using split inside of align
Use empty else block instead of a seemingly superfluous \notag command
Do not define labels globally for flalign and alignat to remove warnings
Change order of commands in test-autonum to avoid font substitution warnings

It does not make a difference in the PDF anyway.
Remove a cref-hyperref warning in test-autonum
Fix remaining warnings in test-autonum by using \ref correctly
Reactivate fixed error when using two labels for the same content
Change \let-usage to support optional argument where useful
Improve consistency of spaces and add more debug information
Add a macro \newcommandsequence in preparation to simplify some code
Simplify definition of \newcommandsequence
Correctly support optional argument of \\

Also use \newcommandsequence to simplify code. Use \detokenize for more
robust tests.
Extend debugging infrastructure
Minor cosmetic improvements
Fix split handling to produce correct vertical space below environment again
Add more detailed information about the position of \label commands