0:00:22.038,0:00:24.606
After breaking Ethic out of prison,

0:00:24.606,0:00:27.821
Hedge flies them both towards [br]a frontier settlement

0:00:27.821,0:00:34.641
in the shadow of the Bradbarrier, [br]the great wall that encircles the nation.

0:00:34.641,0:00:38.973
All the settlers there will soon gather [br]for the monthly feeding.

0:00:38.973,0:00:43.188
The people of the wall spend their days [br]gathering up works of art and literature,

0:00:43.188,0:00:45.788
from all across the land.

0:00:45.788,0:00:50.378
On feeding day, the furnace-bots arrive, [br]ravenous.

0:00:50.378,0:00:56.119
If they eat, the lights stay on, [br]and the food gets delivered.

0:00:56.119,0:00:59.409
If they starve, the people do too.

0:01:00.954,0:01:05.934
Hedge’s fuel supply runs out just as he [br]and Ethic reach the outskirts of town,

0:01:05.934,0:01:08.732
and they come in for a crash landing.

0:01:10.576,0:01:14.996
Luckily, everyone is too busy preparing [br]for the feeding to notice.

0:01:14.996,0:01:17.870
Today’s feeding is where Ethic [br]can find the leader

0:01:17.870,0:01:20.551
of an underground resistance movement.

0:01:20.551,0:01:24.819
This person knows the location of the [br]first of three powerful artifacts.

0:01:24.819,0:01:27.222
The problem is, Hedge and [br]Ethic don’t know

0:01:27.222,0:01:30.618
the resistance leader’s name [br]or appearance.

0:01:30.618,0:01:34.801
But Hedge has gathered the [br]following information:

0:01:34.801,0:01:37.216
The leader has green eyes.

0:01:37.216,0:01:43.236
If the leader has red hair, their name has[br]at least one consecutive double letter.

0:01:43.236,0:01:48.286
If the leader wear glasses, [br]their name has exactly 2 vowels.

0:01:48.286,0:01:52.299
Otherwise, their name has [br]exactly 3 vowels.

0:01:52.299,0:01:57.109
There is exactly one person for whom [br]these are all true.

0:01:57.109,0:01:58.324
As a fugitive,

0:01:58.324,0:02:02.514
Ethic can’t sneak into the crowd without [br]drawing attention to herself.

0:02:02.514,0:02:05.326
But she can give instructions to Hedge.

0:02:05.326,0:02:09.505
And one tool she has is what [br]programmers call a conditional.

0:02:09.505,0:02:13.185
That’s a statement of the form [br]“If A, then B.”

0:02:13.185,0:02:16.376
Flowcharts are great illustrations [br]of how those work.

0:02:16.376,0:02:22.266
This conditional translates to: [br]if A is true, carry out instruction B.

0:02:22.266,0:02:26.178
There are also conditionals that account [br]for different possibilities.

0:02:26.178,0:02:30.025
This says, “If A is true, perform [br]instruction B.

0:02:30.025,0:02:33.718
Otherwise, carry out instruction C.”

0:02:33.718,0:02:38.828
So what instructions does she give Hedge [br]so he can find the resistance leader?

0:02:38.828,0:02:43.492
Pause now to figure it out for yourself.

0:02:43.492,0:02:47.407
With a problem like this, [br]it can help to simplify first.

0:02:47.407,0:02:50.987
What if Hedge just has to examine [br]this one person?

0:02:50.987,0:02:54.232
What information does he need [br]to collect about her?

0:02:54.232,0:02:57.236
He might ask, “Does she have green eyes?”

0:02:57.236,0:03:01.688
What other questions should Hedge [br]ask to find the resistance leader,

0:03:01.688,0:03:05.728
and how can he track those answers?

0:03:05.728,0:03:10.718
Pause now to figure it out for yourself.

0:03:10.718,0:03:14.607
It may seem intuitive how you’d approach [br]this problem as a human.

0:03:14.607,0:03:16.380
But Hedge isn’t a human,

0:03:16.380,0:03:20.990
and so the challenge comes from needing [br]to give him systematic instructions

0:03:20.990,0:03:23.654
that will work in any scenario.

0:03:23.654,0:03:26.578
Hedge needs to examine the settlers, [br]one at a time,

0:03:26.578,0:03:29.139
until he discovers the right person.

0:03:29.139,0:03:32.709
In other words, like with the [br]lock on the prison cell,

0:03:32.709,0:03:36.555
this is a loop that repeats the [br]same instructions.

0:03:36.555,0:03:40.083
Only this time the loop will involve [br]a series of questions

0:03:40.083,0:03:41.770
in the form of conditionals,

0:03:41.770,0:03:45.081
and will end as soon as Hedge [br]finds his target.

0:03:45.081,0:03:48.592
But first, you’ll want to organize [br]your information.

0:03:48.592,0:03:55.130
Each person has a set of characteristics: [br]Eye color, hair color, glasses, and name.

0:03:55.130,0:03:57.297
Does this person have green eyes?

0:03:57.297,0:04:02.367
If so, mark a check next to “eye color." [br]If not, mark an X there.

0:04:02.367,0:04:06.207
If they have red hair, does their [br]name contain a double letter?

0:04:06.207,0:04:09.543
If so, mark a check next to “hair color.”

0:04:09.543,0:04:13.832
If they don’t have a double letter, [br]mark an X next to “hair color.”

0:04:13.832,0:04:18.582
Anyone with red hair and no double [br]letter can’t be the resistance leader.

0:04:18.582,0:04:20.832
But notice that if they have blue hair,

0:04:20.832,0:04:25.432
Hedge will skip this question and [br]go on to the next one.

0:04:25.432,0:04:27.801
For the last question, we can say,

0:04:27.801,0:04:32.551
“If they wear glasses, does their name [br]have exactly 2 vowels?

0:04:32.551,0:04:38.129
If they don’t have glasses, does their [br]name have exactly 3 vowels?”

0:04:38.129,0:04:42.457
There will be people in the crowd with [br]glasses and 1 vowel,

0:04:42.457,0:04:44.864
or no glasses and 2 vowels.

0:04:44.864,0:04:48.673
But they’re not who we’re looking for, [br]so they’ll get X’s.

0:04:48.673,0:04:52.198
The resistance leader must be someone [br]with either check marks

0:04:52.198,0:04:55.027
or blanks next to every question.

0:04:55.027,0:04:58.113
Blanks are ok, because if someone [br]has blue hair,

0:04:58.113,0:05:01.923
the rule about red hair doesn’t [br]apply to them.

0:05:01.923,0:05:05.511
You could have Hedge ask every question [br]about every person,

0:05:05.511,0:05:09.215
and then choose the person with [br]only checks and blanks.

0:05:09.215,0:05:14.165
But there’s a way to save yourself lots [br]of time: as soon as Hedge marks an X,

0:05:14.167,0:05:16.722
have him move on to the next person.

0:05:16.722,0:05:19.294
You don’t need to know the answer [br]to every question;

0:05:19.294,0:05:24.404
just one X means they’re not the target [br]of your search.

0:05:26.283,0:05:28.085
Hedge buzzes through the crowd,

0:05:28.085,0:05:31.646
and within minutes finds Adila, [br]the resistance leader,

0:05:31.646,0:05:33.785
and brings her back to Ethic.

0:05:33.785,0:05:39.055
Adila agrees to help them steal the first [br]artifact— the node of power—

0:05:39.055,0:05:41.018
but under one condition:

0:05:41.018,0:05:43.746
that Ethic and Hedge jump-start [br]the revolution

0:05:43.746,0:05:48.349
by reprogramming the furnace-bots [br]that terrorize the town.

0:05:48.349,0:05:51.129
And right on cue, the robots descend.