To prove: nothing causes itself (where by "cause" here we mean "is the efficient cause of")

Assume:	1.	Something does cause itself.
		Call one such thing "A."
		So the assumption is: A causes A.
Premise:	2.	If x causes y, then x is prior to y.
So:	3.	A is prior to A. (1,2)
Premise:	4.	Nothing is prior to itself.
So:	5.	A is not prior to A. (4)
So:	6.	Contradiction! (3, 5)
So:	7.	The assumption is false. (1-6, reductio)
		I.e., Nothing causes itself.