It turns out that figuring out which 
Wolfram class a particular rule

falls under is not always very 
straight-forward.

Let's look at Rule 10.

If I do "Setup" and "Go",

we see these jagged lines

and these diagonal lines going 
down across the lattice.

Well, it turns out that this is 
considered to be Class 2,

that it's considered to be a 
periodic pattern.

Just because we have this complete repeat
of the pattern at each time step

except that it's translated over 
by a few steps.

So this is considered to be a Class 2 CA.

It's relatively simple.

And if we have a circular lattice,

of course the whole thing will 
repeat eventually.

But the more important things is that
this pattern is repeating itself.

The correct answer for this one was B.

Now let's look at 128.

That one's a little bit easier.

If I now set my rule code to 128,

do "Setup" and "Go",

you'll see that it always goes to a 
white fixed point,

and that's because if we look at Rule 128,

we can see that only an all black initial
configuration will go to black.

So for almost all initial configurations,
this will go to all white.

So the correct answer here, since
it almost always goes to a fixed point,

of all white, we get Class 1.

Now let's look at Rule 22.

I'll set the rule code to 22.

"Setup"

"Go"

Well, it's not clear

whether this is simply periodic

or not.

It turns out that Wolfram classifies this 
as Class 3.

That is, chaotic, random-looking.

Even though we don't exactly have a 
random-looking array,

we have these kind of
triangular structures

but there's no long-lived particle-like
structures as we saw in Rule 110.

So this one was classified as chaotic, al-
though it's not at all trivial to see why.

So I'll mark this down as Class 3,

but don't feel bad if you didn't 
get that right

because it's not obvious to you 
as a casual observer of this

which class this is in.

It's even harder to say what Class 4 is.

This one is pretty vague.

It's hard to say, to tell, 
between Class 3 and Class 4.

and people have joked that Class 4 
are all the cellular automata

that Wolfram himself calls Class 4.