enter image description hereThis is where I get stuck, how do I finish this proof? I only have access to intro and elif rules, not DS or anacon or others.

  • Sorry about that, the picture is added now!
    – Grace
    Dec 6 '19 at 23:29


Your basic idea is correct, but you want to use the exists Elim on the contradiction, this will bring it from the second subproof to the first subproof, so try to find a contradiction inside the second subproof, and use exists Elim on it, this will do the work.


  • thanks so much!
    – Grace
    Dec 7 '19 at 15:40

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