Restricted identity axioms changed

I announced that I have introduces axioms for “restricted identities”, a structure on a category which allows to turn the category into a semigroup (abstracting away objects).

But I noticed that these axioms do not fit into concrete examples which I am going to research.

So I have rewritten the text about restricted identities with somehow different axioms.

The theory of categories with restricted identities is presently presented in this rough draft not yet enough checked for errors. (I am going to move it to the main book after thorough examination.)