Logical System gentzen Quiz 7 Invalidity 10/30/06 Quiz 7 was formerly known as Quiz 4 Quiz 7 Invalidity [This has been done in the downloadable application, but the principles apply to the applet version also.] Your browser does not support html5 video. Book traversal links for Help Q7, invalidity ‹ Help Q7, consistency Up Tutorial 18: Universal Elimination ›