I’m having an issue with problem 6.22. I can prove ¬(b=c) in step 11 by using ¬Intro and citing 3-10, but for some reason Fitch won’t give me the final check for ¬(b=c) in my goal box. Meaning, every step from 1-11 gets the green check but for some reason the proof as a whole does not. Anyone running up against this issue or have an idea about what I’m doing wrong?
I have a question about the homework that was due this morning at 6. For exercise 2.20 Grade Grinder kept giving me the feedback that my proof was correct but didn’t match the steps of the informal proof on page 52. When it says the proof should contain three steps matching the informal proof, I thought that would mean three steps after the Fitch line, so in addition to the three premises. Grade Grinder seems to be telling me that I shouldn’t have three non-premise steps. I’m wondering if the issue is actually about the rules I cited for each steps. Does anybody have an idea about which problem I was running up against? Thanks, Sara