Q4(c)

(4 b is offering some resistance)

I get a "contradictory" solution again.

1. Forall-x (~P(x) && Q(x)) ...... premise
2. box-1 ... The arbitrary x₀ plus ~P(x₀) && Q(x₀) ........ forall e, 1
3. ... ~P(x₀) .......... && e, 2
4. ... box-2 .. P(x₀) .............. assumption.
5. ... .... "bottom" ......... ~e 3,4
6. ... .... Q(x₀) ......... "bottom" e, 5 .... end of box-2.
7. P(x₀) -> Q(x₀) .......... -> i, 4-6
8. Forall-x (P(x) -> Q(x)) .......... forall-x i 2-7

(For some arbitrary x-value we get the implication. Then we must get it for all x-values).

Ok, here's my attempt:

1..... For all x (~P(x0) & Q(x0))
2... x0 box
3.... P(x0). Assumption
4. ~P(x0) & Q(x0). For all x e 1
5. Q(x0). & e 1
6.... P(x0) --> Q(x0). --> 3-5
7.... For all x P(x) --> Q(x). For all x I 2-6

Sorry line 5 I meant & e 4

Yours is cleaner, but I think mine works, too?

Careful with line 1. Obviously it's just a "slip of the pen", but I'd imagine that kind costs.

I think you could cut it down to 6 lines, even, if you instantiated at the same time as opening the box. Some little warning about these boxes in the notes rings a bell here, though. There was something the text book was not doing right that I still have to find in the notes, when it came to these instantiations. Do you recall anything like that?

To be honest I was completely lost with proofs till my assign came back and the lecturers comments helped clear up a lot of confusion. My year mark is not so pleasant and I'm guessing I'll hav to work really hard to get a distinction or perhaps even a pass with this course.

Well you look like you've gotten it pretty much sorted since then? Your proofs here are all correct at least. Me, I'm long past hoping for distinctions. The year is not one of those that permits such things. Survival will put a big grin on my face, I tell you. I might even dance a little jig.

what courses you doin nxt sem? If you have decided yet. I got 4 more nxt sem and den I'm done wid my degree. I'm thinking of doing INF3703, INF3705, COS3711, COS3751.

Advanced programming, Graphics (for COS)

And then SystemsDev (Y3), and HCI 2.

(I just want to get finished first. Suspect I'm not on the "honours list", so might complete COS by taking AI next year NDP. A bridge to cross upon arriving there...)