.  As Q Chris said, "...9 is clearly marked as a premise and so does not follow any other," therefore, one cannot use 9 to disprove 1, 2, or 3, since they have no logical inter-dependence.  The fact that premise 9 creates a contradiction only proves that the argument, assuming premise 9, is invalid.  It would be perfectly valid, though incomplete, assuming only 1, 2, 3.  Again, Reductio ad Absurdum arguments show that "not all premises can be true," not that "all premises are not true"