And then upload.

So let me share my screen.

We're going across.

Pardon me.

I didn't understand you.

Okay, so we were talking about first logic. First logic is kind of at the other end of the spectrum of world description languages that we're going to look at.

Much of this logic we already know.

We've kind of had a preview of what first of the product logic is.

With peeling Q and we want to be able to talk about things like all blocks are read.

All the blocks are.

On the table in this situation or.

That's a D is a block and we want to infer from that.

That D is on the table and that D is is read and we're going to use a logic.

First order predicate logic where we can write down things like block effects.

Okay, there is something in the check.

Okay, yeah, the computer voice good.

So if you have questions, zoom has the advantage that we can actually just that you can just talk and I'll try my best to answer that.

So a logic which talks about individuals, their relations, their properties and maybe even functions and we can talk about unique existence and universality.

And we can already see that if we invest more in to a.

More expressive language, then our world descriptions may become.

Smarter rather than having to talk about every single.

Cell and what the one does to the neighboring.

To the neighboring cells, we can just basically say something like for all X effects is a one plus then in all of the.

For all cells X, if there's a one percent X, then in all the assumption in all of the adjacent.

Cells, there is a stench just essentially like the natural language description of the walls.

We can talk about infinite domains, which is very important, and we can even.

We can even talk about big parts of math using first order logic, which is, by the way, why math has adopted first order logic as its official language of inference.

Right.

We.

Have.

That's kind of the motivation so far, and now we get into the technicalities for first or logic.

Is more complicated than propositional logic, but it uses all the bits and pieces we've already looked at, so we have the connectives from.

Proposition logic, we have not and or and and and implies and so on, we think of them as functions on the truth values, we have function constants, we have predicate constants and we will eventually need something which we're going to call scolum constants.

Which are a supply of.

An infinite supply of function constants that we are going to use for for inference.

They will kind of be introduced in inference, but not in describing the world.

And all of those things which we kind of put together in what we call a first order signature.

Are things we've already seen in PLN queue and propositional logic.

The first real new thing we do is we also assume a set of individual variables we call them X, Y, Z and so on.

And kind of what I what I try is to kind of keep them.

Keep them capitalized.

Like we like we do in prologue and again we.

We need a countably infinite.

Set of variables, because we never want to run out of them.

From those we build up terms just like in PLN queue propositions just like in PLN queue.

The only thing that we do a new is we have a set of variables.

Just like in PLN queue.

The only thing that we do a new is if it is kind of sitting here.

If A is a proposition.

Then for all XA is also a proposition.