It never ceases to amaze me how people want to teach others to fly even before they can crawl. Sigh. Funny that my answer is so far the only one that tries to give a simple explanation that is still mathematically rigorous.

@user21820 this might be off topic but how long do you think it should take to finish the whole book that you recommend?

Hello, @user21820 ! My trip was longer than expected. It started more than 3 months ago, and due to the pandemic, I am not returning home. Fortunately, I can get (low-speed) Internet in this little town from time to time.

@user21820, I would like to continue studying full FOL with you. Should I start learning LPL from zero and then attempt the exercises you posted here ? I have that book and I think it is interesting. What do you recommend, taking into account that some time has passed and that I will have to review some of the things I learned ?

@eryceriousmatherfunker It really depends on your background. You should skim through as quickly as you can, but making sure that you have 100% grasp of the logical reasoning behind the deductive inferences. Actual terminology does not matter. At the end you still have to work through some exercises for me to know whether you grasp basic FOL or not, so that I can tell you where to go from there.

@F.Zer Ahh it's great to hear from you. I don't think you need to go through LPL, because it's at a lower level than you are at now. Yes, you would probably have to review what you've learnt a little bit, but I don't think you'll actually have forgotten how to use the deductive rules (even if you forget what exactly the basic rules are).

So I think it's best for you to just continue working through the exercises I last gave you. I think you haven't done any of Q6 to Q10 yet.

Any good book that someone can suggest me..