Hi there

I've been working on this question for most of yesterday and all of this evening and I'm stuck. I'm using Fitch to tell me if the proof is right and I just can't seem to get it.

I've tried to use two subproofs, one for Cube(c) and one for Dodec(c) but I don't get anywhere with that. Then I tried a subproof for the assumption of b=c, which I can get to a contradiction but then I don't know what to do next.

1. Cube(c) v Dodec(c)

2. Tet(b)

----

3.1 b = c

----

3.2 Cube(b) v Dodec(b)

3.2.1.1 Cube(b)

----

3.2.1.2 (contradiction)

3.2.1.3 ~(b = c)

3.2.2.1 Dodec(b)

----

3.2.2.2 (contradiction)

3.2.2.3 ~(b = c)

3.3 (contradiction)

4. ~(b = c)

Fitch doesn't like the steps 3.3 and 4. And I also have a feeling I'm going about this all wrong - because this question is worth 8 points in comparison to 2.1 being worth 10 points, which I did in fewer steps than this...

Please could someone point me in the right direction.

Thanks,

Rachel

PS: does anyone know where I can find out more about the error messages that you see when you get a reason wrong in Fitch?