In any event, I assume that at least one rule exists, directly or indirectly: you cannot travel backwards in Creation time by taking a hop through Void. Doing that would lead to all sorts of problems, grandfather paradoxes, and what have you.
That's not an assumption. It's the truth.
I believe the reason we agreed on is that the past is a concept, nothing more. Trying to travel to the past is like trying to travel to pie (not as in a pie, as in, literally, pie).
You can, however, travel to a specific pie. Can you travel to a specific past?
No, because pie has actual instances of pies. Past is a concept only.
Hardly. There are specific pasts. Five minutes ago, fifteen, an hour ago, last week, two years ago, the last time I went to the planetarium, the Renaissance...
That still isn't an accessible instance.
Why not? Your logic is that you can't go to the past because it's a concept (like pie), not an instance of a concept (like that specific apple pie). So why can't I travel to a specific past?
at Aphestadil levels of summoning, the circle is more or less just a fomality.
What about other summons?
Well, some magic works through words and runes of power; you have mundane languages, which have words resembling an object or aspect, then you have a magic language, which has words actually for an object, and can incant the word to control said object or aspect. If you've ever read the Inheritance Cycle by Paolini, sorcerers and the such use magic this way. For example, the word Brisingr is for fire in the books, and can be incanted to control fire. More complex spells need phrases put in to give the spell specific instructions. The magic language has a name, but it is not known. If one did know the name, then they could control everything and thus have the power of a god.
Spoilers are involved in expanding on that last point.
Anyways, this leads to several questions. Like why the language of everything is conveniently pronounceable by humans, or how it can be converted to diagram format.
Son Goku disagrees
an we'll see who wins in a fight, Lunette or Son Goku
"Gandhi thinks conquering and oppressing people is wrong. Ghengis Khan disagrees. We'll see whose army is stronger."
Who wins in a fight depends more on strength than tactics, when the difference in power is that severe.
behold the power of yelling loudly for 20 minutes to gather your energy being a grown man with superhuman strength and toughness beating up a little girl
FTFY.