So I will show you where currently lies my problem. So, I’m trying a reduction but I’m not seeing how to get the contradiction. I’m guessing that I’ve to get a proposition telling “ ~ (b =a)”, but I’m not seeing how.


https://www.dropbox.com/s/nw0cmgx0bqvybml/IMG_0059.JPG?dl=0

Yes.

It's precisely that!

Oh... my bad (I'm portuguese, by the way, so some errors in my english are possible).

<-> is the conective for the logical equivalence. So in the exercise "y = x <-> Gy" is "y is equal to x if and ony if y is G".