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Question: is it possible to tell Maple not to re-write arccos(a-b) depending on letter ordering?

Question:is it possible to tell Maple not to re-write arccos(a-b) depending on letter ordering?

nm 8552 Maple 2020
ordering canonical
July 12 2020
1

I was just praising Maple for not rewriting/simplifying  expressions automatically without the explicit user asking for it, when I found the following strange result

expr:=arccos(a-p) does not cause any change in the input. Good.

But when I change the letter ordering to expr:=arccos(p-a) now Maple changed it to Pi - arccos(a - p)

I have no idea why. Is there an option to tell Maple not to do that, even if it is mathematically correct? 

restart;
expr:=arccos(a-p);

restart;
expr:=arccos(p-a);

It seems to use lexicographical ordering to re-write things. Is it possible to turn that off?  Notice that I did not ask for simplification or anything. 

Maple 2020.1, Physics 724
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