Where do the terms "Law of Wheels/Cycles" come from? In Puella Magi Madoka Magica, before Ultimate Madoka's universe, I read that the system where a Magical Girl would become a Witch was referred to as the "Law of Wheels", while after that, the new system and Madoka herself is known as the "Law of Cycles", this term actually being used by Homura and the Incubators in the Rebellion movie.

I am wondering, where did these terms come from? Neither system seems like a wheel/cycle as in neither one does a Magical Girl ever return to normal (the origin).

EDIT: I seem to have made a mistake as Mami may have said "Law of Wheels" in Episode 12 in Ultimate Madoka's Universe, but still it doesn't change my question of where these terms came from.
By interview of Gen Urobuchi, Law of Wheels/Cycles is a folklore talked between Magical Girls.

Following idea is my (and some Japanese anime fan's) guess.

Law of Wheels/Cycles is translated from "円環の理".
理 is principle or reasonable.
I think 円環 is circle or ring instead of Wheels/Cycle.

Madoka is officially written as "まどか", but most Japanese have a name in kanji.
By a naming dictionary,
most common kanji for the name "まどか" is "円"(circle).

By this two facts, I guess 円環 means Madoka.
In the rewritten world, most people forgot about Madoka, but Homura found some affected things from Madoka.
I guess the folklore was named Law of Wheels/Cycle because of such a effect.