I posted this on math help boards:
...but I didn't know how active that site was. Feel free to reply on there as well as here.
This is my question:
Give a formal proof to show
I'm new to these, and this one looks like it should be easy.
What I want to do is:
1). substitute x into where there are already x's.
2). Make the statement valid for all y
3). substitute y into 0' and y' into 0''.
3). Since it's valid for all y, choose y to be 0.
Here's what I did:
1 (1) Assumption
1 (2) Universal Elimination rule
1 (3) Existential Introduction, 2
4 (4) Assumption
1,4 (5) Taut 3,4 <--- ?
1 (6) Existential Hypothesis, 5
I think i've got the right idea, I think the execution starts to go wrong at around line (4).
Does anyone have any ideas?