Logicola 3
medium.com
medium.com
If you’d like, I can send you an email with the contact info of the person I talked to. Feel free to send me a Discord message (I’m my HN username with a single dot before it there).
(R ^ L) v N <- incorrect
((R ^ L) v N) <- correct
((S -> G) v H) <- correct
(S -> G) v H <- incorrect
These pairs are the same, the extra parentheses don't change the meaning of the statements but only the ones with the extra parentheses are marked as correct.The language he uses requires the extra parentheses whenever using any of v, ^, ->, or == (and, or, implication, equivalence/iff). This is probably a reasonable thing in context because it means the expressions can be cleanly combined as written and probably avoids confusion for students. They don't have to learn a precedence order.
So if a student ever arrives at these pair of statements:
(P v Q)
R
And they use and introduction they'll get: ((P v Q) ^ R)
No ambiguity, just combine the two as written and wrap in parens.So I'll retract my previous feedback.
I remember also asking him if it could be derived with constructive logic rather than by contradiction. He didn't have a fitch proof of that sort but thought it should be possible.
https://www.amazon.com/Godels-Theorem-Simplified-Harry-Gensl...
This was in the late 90s / early 2000s so well past the DOS era but old DOS apps were still in use here and there (and would still run on Windows).
Also, on the front page there is a link to logicola.com, which is a typo, I think.
Finally, I'm using ff on windows with a screen reader and when I press the chapters button on the web page, absolutely nothing happens, so it is not clear how I'm supposed to test the website.