So, first of all, I need to comment on the exercises.

So, unfortunately, I was not clear enough or I didn't tell the right thing in the right place and in the right time.

But several people didn't understand.

I mean, in particular because they were just missing when I said this.

That I want the exercises to be handled back before we start the practicals.

So, some people didn't manage to do it in time.

And they worry that if I don't count them, then it would have a big impact on the end note.

And indeed, probably it will because, as I said, basically the exercises contribute half of the note.

And there are probably not going to be so many because they appear just once in two weeks.

So, I propose that we just count it as a rehearsal and start counting points from the next time on.

Hopefully, now everyone is up to date with the idea.

I also made an announcement at the webpage and read saying that it's before 10 a.m.

It's not 12 p.m. It's not anywhere on earth like tomorrow's 1 a.m. or something.

Yes.

10 sharp or 10.50.

Yes, I put it at 10 sharp.

Yes, just in case.

Okay, so 10.50 is actually right.

Right.

So, okay.

And what else?

Concerning the next exercise, it's published.

You can look at it.

And I really recommend you that you get familiar with it as soon as possible because, I mean,

I'm giving two weeks for that.

And if you postpone it until the day before the submission, it's probably not going to work

because there is some work to be invested.

So, if something is unclear, something needs to be commented, please try to ask me about

it as soon as possible.

And presently, I mean, my goal for today is basically give you enough background for solving

this exercise.

This is my ambitious goal.

So, there are two exercises, the first and the second, which I hope you can solve already

because, I mean, there is information for that.

But the third one is wastely missing, the material.

And I'm going to give it today.

Right.

Another thing I wanted to mention is correct, again, myself.

I claimed erroneously again that this Y operator for call by value need to have this type.

This is too restrictive, actually.

It's sufficient that it has this type.

So, this A and B need not be the same.

I don't know why I made this mistake.

But apparently, the argument which I gave why we need it, it applies to this constructor

just as well for the same reason.

And I've corrected it on this PDF file which I published on the webpage.

Okay.

So let's go to the material of the lecture.

And as I said, we're going to reuse the operator, this let operator.

And first thing that I propose you to note here is that this P is something of type A