Cave scanning order effects or "Safely touch fireflies!

Dustin · Post by **Dustin** » Sun Jun 28, 2020 9:57 pm

You're welcome, zsom!

Episode 11 - Who killed Rockford?
I just had the idea for some puzzle mysteries that can be solved with the knowledge from this thread - can you solve them?

Mystery 1
Rockford has exploded! The police find three fireflies left at the crime scene. They reconstruct the case, and the initial situation turns out to be as follows:
TTTTT
TFFFT
TFIFT
TFFFT
TTTTT
T=Titanium Wall, F=Firefly, I=Inbox where Rockford comes out
Well, one thing was perfectly clear: When Rockford came out of the inbox, he didn't have the slightest chance to escape! Immediately he got crushed by the cunning fireflies! But two question remained:
1. Which of the eight fireflies actually killed Rockford?
2. Which three fireflies survived the explosion?
You're the detective! Can you figure it out with help of the cavescanning order?

Mystery 2
DDDDD
DDFDD
DFDRD
DDFDD
DDDDD
This time, Rockford Rockford made the fatal mistake himself. In this situation, he accidently stepped to the left - it needn't be explained further that this was no good idea! There was a big bang and in the end, only one firefly survived the accident. Which one was it?

Mystery 3
TTTFTTT
TTTSTTT
TTTSTTT
FSSRSSF
TTTSTTT
TTTSTTT
TTTFTTT
Rockford really wasn't careful here either, and so he got ambushed by four fireflies which all faced toward him. Rockford didn't move at all - it would have been too late anyway - and a second later he was blown up by... which firefly? And which fly survived to tell the story?

Have fun with these cavescanning-order-riddles! Feel free to post your suggestions if you want! Solutions probably next weekend!

zsom · Post by **zsom** » Mon Jun 29, 2020 8:09 am

Hi
First task
The first thought was that Rockford would be killed by the No. 2 skylight, the one above Rockford's head, and there would be three skylights downstairs ...
However, in the Gdash editor I drew this position and the skylight No. 5, the one to the right of Rocford, exploded, the three skylights on the left of Rockford survived.

I don't know why this happened

zsom · Post by **zsom** » Mon Jun 29, 2020 8:27 am

Second task
The first thought was that Rockford would be killed by skylight # 3, the one below Rockford.
Because when Rockford moves left, the first skylight will be scanned, the second will also be scanned, and kill the third one.
In the Gdash editor I drew this position and it turned out that I was thinking correctly;)

zsom · Post by **zsom** » Mon Jun 29, 2020 8:35 am

Third task
Knowing the answer to the first riddle, I suspect Rockford will be killed by a skylight on his right.

Have a nice day

Dustin · Post by **Dustin** » Sat Jul 04, 2020 5:50 pm

Episode 12 - Solutions to the riddles
First of all, thx zsom for your solutions! My week was fine, hope yours too!

So let's analyze the riddles one by one!

Mystery 1
TTTTT
TFFFT
TFIFT
TFFFT
TTTTT
T=Titanium Wall, F=Firefly, I=Inbox where Rockford comes out
The question was - who will kill Rockford as soon as he comes out?
zsom, your solution is very interesting, and I also thought first that the firefly on top of Rockford should kill him because this firefly is scanned first in every frame! So why is this wrong and why does the firefly to the right side of Rockford explode instead? Let's see:

First of all, it's important to note that Rockford is invincible until he has fully come out of the inbox and can move! After the "starting shot" that can be heard when Rockford comes out of the inbox, there will be another 4-5 frames until Rockford can move, and during these 4-5 frames he's still invincible!

So the interesting moment is the frame when Rockford fully comes out! Let's analyze this frame:
TTTTT
TFFFT
TFRFT
TFFFT
TTTTT
Note that in this picture, Rockford is still invincible as he has not fully come out yet! He will only do so when it's his turn to be scanned!
Cave scanning order:
1. The top-left firefly is not dangerous.
2. The top-middle firefly touches Rockford. However, it does not explode because Rockford is still in his invincible state!
3. The top-right firefly - no danger.
4. The left-middle firefly also touches Rockford but does not explode - see 2.
5. Now it's Rockford's turn! Now his state changes from "partly out, invincible" to "fully out, fully controllable, but also vulnerable"!
6. Next comes the right-middle firefly. It touches Rockford, who is no longer invincible! So here we have it - the firefly explodes!

That was a difficult one! Let's summarize the solution:
The right-middle firefly kills Rockford because it's scanned directly after Rockford has fully come out of the inbox! Consequently, the three fireflies at the left survive!

Mystery 2
Congrat zsom, your solution is indeed fully correct!

DDDDD
DDFDD
DFDRD
DDFDD
DDDDD
If Rockford accidently moves left here, then the bottom firefly is the one who explodes because this firefly is scanned first after Rockford moves! Consequently, the top firefly is the one who survives.

Mystery 3
TTTFTTT
TTTSTTT
TTTSTTT
FSSRSSF
TTTSTTT
TTTSTTT
TTTFTTT
This was the initial situation. As Rockford does nothing, two frames later we all 4 fireflies will touch Rockford simultaneousely:
TTTSTTT
TTTSTTT
TTTFTTT
SSFRFSS
TTTFTTT
TTTSTTT
TTTSTTT
The cavescanning order now says that the top firefly is scanned first and kills Rockford. Consequently, the bottom firefly survives.

zsom, I think you did quite well - the only thing that confused you was the inbox exceptionality in mystery 1! Your argumentation for mystery 1 would, however, have been perfectly fine in mystery 3!

So in the next episode, we will continue analyzing caves - cave 9 with the first amoeba is next! So in this episode, we will discuss our slimy friend in quite some detail!

Dustin · Post by **Dustin** » Sun Jul 05, 2020 5:29 pm

Episode 13 - cave 9 analysis
From now on, I'll use real pictures for this thread instead of ASCII arts!

Thx Arno for hosting the pics on the site!

https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 9 ("Trapped") starts at 2:28.
Here's the cave map - first picture!

What do we see?
There's a silent amoeba at the start which has nowhere to grow yet doesn't convert into diamonds. Rockford blasts one of the two growing walls, so that the other grows back and traps the amoeba again, and now it does convert so the cave can be solved. Also interesting - Rockford pushes a light boulder over empty space!

How does it work?
I think this cave could bring up several questions, so let's analyse them one by one:

1. Why does the amoeba not convert immediately into diamonds?
This has nothing to do with the cavescanning order - it's because the amoeba is "dead". A dead amoeba is an amoeba that is trapped from the beginning. Dead amoebas do not convert nor make any noise. As soon as the amoeba gets a possibility to grow, it becomes "alive", which is how we usually know amoebas - they make noise, grow unpredictably and can convert into diamonds or boulders! So this defines Rockford's task in this cave - the dead amoeba must get a possibility to grow so it becomes alive, and then it must be trapped again so that it converts into diamonds!

2. Why don't we simply blast both growing walls simultaneousely?
If we did this, then the amoeba would also become alive, but we wouldn't have a possibility to re-trap it afterwards! The only possible way would be to wait until it fills the whole cave, but for this solution, the timer is too short!

3. How can the light boulder be pushed over empty space?
Now it becomes really interesting w.r.t. our topic!

First of all, what is a light boulder anyway? That's just a boulder without pushing delay, so it can always be pushed if Rockford wants to. So let's see how Rockford pushes the boulder over empty space:
Frame 0

Cavescanning order:
1. Rockford is first. We move right, thereby pushing the boulder. If it was a normal boulder, we would only have a 25% chance of success, but with a light boulder the engine says "ok, no problem!", so the boulder is pushed.
2. The boulder is scanned next. But it has just been pushed, so it cannot move again in the same frame. (That's a rule I wrote down in episode 3 but we didn't use it often, so maybe you forgot about it in the meantime!)
3. The amoeba stuill cannot grow and stays "dead".
4. The firefly moves up.
Frame 1
Oops, I forgot this picture!

Ah well, it shouldn't matter that much - the important thing is that Rockford is still at the left side of the boulder. That means Rockford is again scanned first and can again push the boulder before it falls down!
With this reasoning, Rockford could push the light boulder to the right as far as he wishes over empty space! However, pushing to the left side over empty space is not possible - then the boulder would be scanned first and fall down before Rockford could push it.

4. How does the amoeba come to life although the growing wall grows back immediately?
Another cavescanning order issue - let's especially analyze the frame when the smoke from the firefly explosion is just about to vanish:

Cavescanning order:
1. Rockford is first. It doesn't matter what he does here.
2. The three upper pieces of smoke vanish one by one.
The same goes for the three middle pieces of smoke.
3. Next is the growing wall. It cannot grow because there's still smoke in the way!
4. The bottom-left piece of smoke vanishes.
5. The outbox does of course nothing.
6. The last piece of smoke vanishes, too.
7. Now the left piece of amoeba. It cannot grow.
8. But the right piece of amoeba can! It can grow upwards, where the smoke has just vanished! This possibility to grow is what the amoeba needed to come into life - you can hear its typical sound for a short time in the video if you listen carefully!
The probability that the amoeba actually does grow is very small, but the decisive thing is that it got the possibility to grow so it changed its state from "dead" to "alive". Now we have a "pretty normal" amoeba, which means that when it's trapped again by the growing wall, it will convert into diamonds, these diamonds fall through the slime and the rest is trivial!

5. BTW - why isn't the outbox harmed by the firefly explosion?
That's a specific feature of the engine at Krissz's boulderdash site and has nothing to do with cavescanning order issues.

6. Couldn't Rockford do the firefly blast at the left side? Wouldn't it be the exact same thing?
Why push the boulder over empty space? Why not just blast the firefly like this?

Well, I leave this question to you! Feel free to make a cavescanning-order-analysis of this frame...

...analogous to our analysis above to see the differences! (Once again, the smoke is in its last phase so it's about to vanish.)

Next, we'll see another amoeba, and a seemingly untrappable one, but Rockford manages to block two spots at the same time!?!?

Dustin · Post by **Dustin** » Sun Jul 05, 2020 5:56 pm

Ah, I almost forgot it - ten new caves can be viewed on Arno's YouTube channel!
https://www.youtube.com/watch?v=0YD_THGGhVw
Some of these caves might make you think that everything we learned so far was wrong!

But in fact, these caves use very specific open-border-effects that we haven't discussed at all so far!

zsom · Post by **zsom** » Mon Jul 06, 2020 5:47 am

Good morning to all BD fans!
Hi Dustin
Hi Arno

A lot of interesting information about amoeba and stone.
I made this cave in the Gdash editor, the first version of the game was unsuccessful.
In the second version I added an additional element, sweet ... and then I managed to kill a fly.
However, I also broke the exit.
I have a replay of this in the .bd file that plays Gdash. Can this file be shared on the forum here?

best regards

Dustin · Post by **Dustin** » Mon Jul 06, 2020 9:17 am

Hi zsom!
Yes, with the GDash engine, the exit will get broken when you kill the firefly, so this cave would be unsolvable. The easiest way to solve this problem is to just place the exit somewhere elase, where it's far away from the action! Then everything should work fine.

I've started to remake all the caves in GDash, too, but I have only made caves 1-19 so far. If you like, you can pm me your email and I'll send my GDash file to you!
Cheers

Dustin · Post by **Dustin** » Mon Jul 06, 2020 8:42 pm

Episode 14 - cave 10 analysis
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 10 ("Quantum Rockford") starts at 2:43. Here's the map:

What do we see?
It seems that the amoeba can not be trapped - there are no boulders in the cave and Rockford alone isn't big enough, it seems. But suddenly, Rockford seems to be at two places simultaneousely, so the amoeba gives up and converts into diamonds!

How does it work?
Clearly, the interesting stuff happens shortly before the amoeba converts:

Cavescanning order:
1. The upper half of the amoeba is scanned piece by piece. None of the amoeba pieces can grow, as everything is blocked by amoebas, titanium walls, and - last but not least - Rockford himself!
2. Rockford is scanned next. He moves down, as we see in the video.
3. Now the bottom half of the amoeba is also scanned one by one. And - magically - each piece is trapped here as well!The rightmost piece of amoeba is blocked by Rockford, who has just moved in the way!
So after the cavescan finishes for this frame, every amoeba piece was blocked and could not grow. So the amoeba changes its state from "alive" to "trapped" and the usual thing happens - it converts into diamonds!

So how could Rockford block two amoeba pieces simultaneousely?
--> The top-right amoeba piece was scanned before Rockford moved down, so it was blocked by Rockford.
--> The bottom-right amoeba piece was scanned after Rockford moved down, so it was also blocked by our hero!

And that's how the cavescanning order allowed Rockford to do the impossible thing - he blocked two amoebas in one frame!

So what's next after we discussed all the caves from the first video? Well, there's still a lot to discover in the other four videos! I don't know yet whether I want to discuss each and every cave in detail, as by far not every cave has something really new to us. Perhaps some of the caves are quite good interactive exercises! Also, maybe it's time for a wrap-up about what we've learned so far?! Let's see - in any case, I still enjoy writing in this thread, so the next episode is just a question of time!

Dustin · Post by **Dustin** » Sun Jul 19, 2020 8:22 pm

Episode 15 - The cavescanning order quiz!
Now that I've analysed and explaines ten mini caves in detail, I think it's a
good opportunity for a little quiz! I've prepared 12 multiple choice questions.
Some of them just demand 1:1 reproductions of what we've learned so far,
others are trickier! There's no special order in which I give the questions.
Solutions in the next episode! Have fun!

Question 1

(IN=Inbox where Rockford comes out)
In which direction can Rockford safely move to escape the fireflies?
(Snapping is not allowed!)
A Up
B Left
C Right
D Down

Question 2

Which boulder will kill the firefly?
A The top-left boulder
B The top-right boulder
C The bottom-left boulder
D The bottom-right boulder

Question 3

Which diamond(s) can Rockford collect and still reach the outbox?
[Remark: The facing directions of both flies are such that they will keep spinning in their 2x2 cage.]
A None
B Only the left diamond
C Only the right diamond
D Both diamonds

Question 4

How should Rockford best solve this cave? (1 diamond is required.)
A Move to the diamond's left side and snap it.
B Move to the diamond's left side and move right.
C Move to the diamond's right side and snap it.
D Move to the diamond's right side and move left.

Question 5

Which firefly will be killed if the amoeba doesn't grow?
A None
B Only the left firefly.
C Only the right firefly.
D Both.

Question 6

Is it possible to trap the amoeba, assuming that it doesn't grow within the
next few seconds and further assuming that the time limit is too short to let
the amoeba fill the cave?
A No, it isn't.
B Yes, Rockford must help to trap the left amoeba.
C Yes, Rockford must help to trap the right amoeba.
D Yes, both is possible.

Question 7

Can Rockford convert the boulder?
A No, the growing wall will block the boulder off.
B Yes,if Rockford pushes the boulder left.
C Yes, if Rockford pushes the boulder right.
D Yes, both is possible.

Question 8

Rockford has already collected enough diamonds, but on his way to an
outbox, a firefly chases him closely!
Which outbox should Rockford head for?
A Top-left
B Top-right
C Bottom-left
D Bottom-right
E It doesn't matter - Rockford explodes immediately!

Question 9

What can Rockford do to survive?
[Remark: Note the facing directions of each firefly!]
A Move up
B Move left
C Move right
D Move down
E Stand still

Question 10

Is this cave solvable with 1 diamond required?
A Yes
B No

Question 11

Which of the following things can Rockford do without getting blocked by the
growing wall?
A Move up and immediately down again
B Move right and immediately left again
C Move down and immediately up again
D None of the above

Question 12

Which of the following things can Rockford do without getting blocked by the
growing wall?
A Move up and immediately down again
B Move left and immediately right again
C Move down and immediately up again
D None of the above

YouTube · Post by **Arno** » Mon Jul 20, 2020 8:12 pm

Nice quiz! I did all the questions; very funny!

Dustin · Post by **Dustin** » Fri Jul 24, 2020 3:35 pm

Thanks Arno! You'll soon know whether you got everything right, but I think I
want to make some more pictures to explain some of the correct answers, so
the solutions will follow in one of the next episodes!

For now, I'll continue with...

Episode 16 - cave 11 analysis
This is the start of the second video:
https://www.youtube.com/watch?v=7-3oOxrxLD8

Here's the cave map:

Cave name: "Schrödinger's Magic Wall"

What do we see?
Rockford needs 1 diamond, which, obviously, must come from the amoeba.
But the time limit is much too short for the amoeba to be trapped! So what to
do? The video shows the amoeba converting seemingly "out of nowhere" -
only the melody tells us what's going on: it seems that a magic wall has been
activated and stopped the amoeba! But no magic wall can be seen - how is
this possible?!

How does it work?
The above cave map shows you the truth - actually there is a magic wall in
the cave, and it gets activated and destroyed in the same frame, so it
can actually never be seen!
As the main action happens in just one frame, let's analyse this very frame in
detail:

Frame 0

That's the situation directly before the amoeba converts. What happens now?
Cave scanning order:
(The first two rows with just walls, dirt, space and the passive boulder are
uninteresting.)
1. Rockford is scanned, but he's not part of the action this time!
2. Now comes the (falling) boulder to his right. The boulder "sees" the magic
wall below it, so it activates the magic wall and at the same time
vanishes.
3. The slime is irrelevant for the action in this frame.
4. The top piece of amoeba is next. What happens? Well, the engine
remembers that a magic wall has just been activated, which means that every
amoeba should convert into diamonds! So that's what happens - the amoeba
converts!
5. The magic wall is next. Nothing happens here. (The BD engine is
programmed such that a magic wall gets activated by a boulder falling
through it. So, actually, when the magic wall itself is scanned, nothing
happens!)
6. The falling boulder next to the magic wall is scanned. It "sees" the firefly
below and kills it. This explosion also destroys the magic wall!
7. Finally, the bottom three pieces of amoeba turn into diamonds as well.
(The firefly would be the last element to be scanned in this frame, but it
already got crushed!)

So a lot of things were going on in just one frame, and the next visible
picture is:
Frame 1

(Actually I forgot to edit four pieces of smoke from the firefly explosion - just
imagine they were there! ;D)
The amoeba got converted by a magic wall that could never be seen!

Let me summarize:
With the above analysis, we have seen that the magic wall activation (step 2)
happened before the explosion that destroyed the magic wall (step 6). That's
the reason why the magic wall could convert the amoeba before it got
destroyed. On the other hand, as all this happened within the same frame,
the magic wall was never visible in the video - so if it weren't for the telling
sound, it would truly look like the amoeba got converted "out of nowhere"...

Dustin · Post by **Dustin** » Sun Jul 26, 2020 6:45 pm

Episode 17 - Solutions to the quiz
!!!SPOILER WARNING!!! If you haven't tried the quiz yet - see episode 15 -
you might want to try it yourself before reading the solutions!

So here are the answers and explanations! Let's go!

Question 1

(IN=Inbox where Rockford comes out)
In which direction can Rockford safely move to escape the fireflies?
(Snapping is not allowed!)
A Up
B Left
C Right
D Down
Explanation: That's a cavescan-order-trick that most BD fans know! We
discussed it in detail in episode 1.

Question 2

Which boulder will kill the firefly?
A The top-left boulder
B The top-right boulder
C The bottom-left boulder
D The bottom-right boulder
Explanation: C and D are clearly out of question, and the cavescanning order
decides between A and B.
In the first frame after the given picture, not much has happened - the firefly
just moved down by one step:

In the next frame, both boulders in question are scanned before the firefly,
which means the firefly is still in their way. So, again, only the fly moves:

And now, in the next frame, the top-left boulder is scanned first, and it can
finally start falling, which makes answer A correct!

Question 3

Which diamond(s) can Rockford collect and still reach the outbox?
[Remark: The facing directions of both flies are such that they will keep spinning in their 2x2 cage.]
A None
B Only the left diamond
C Only the right diamond
D Both diamonds
Explanation: That's a tricky one! First, let's try to get the left diamond.
Collecting it is not a problem, but the way backwards is:

Here, Rockford cannot start moving yet. If he moves down in this situation,
the cavescanning order is against him:
1. Rockford is scanned first and moves down.
2. The firefly is scanned next, sees Rockford beside it and explodes.
So Rockford must wait for one more frame and only then start running.
However, this will lead to the following situation:

Rockford touches the firefly from its right side, which is always lethal,
because the fly will be scanned first and explodes!
Rockford can try other strategies, but nothing works - he's stuck in the corner
and will never reach the outbox! So there's no way to get the left diamond
and come back again!
What about the right diamond? Isn't it just the same story here? No! Again,
it's easy to get to the diamond, and on his way backwards Rockford starts in
this situation:

Two frames later:

And here's the difference: Rockford now touches the fly from its left side! This
means that Rockford is scanned first and escapes!

Question 4

How should Rockford best solve this cave? (1 diamond is required.)
A Move to the diamond's left side and snap it.
B Move to the diamond's left side and move right.
C Move to the diamond's right side and snap it.
D Move to the diamond's right side and move left.
Explanation: B and D lead to immediate explosions. C is possible, but there's
a 50/50 risk that the firefly will come out immediately and kill Rockford (see
episodes 1 and 2). This leaves A as the only way to solve the cave without
luck!

Question 5

Which firefly will be killed if the amoeba doesn't grow?
A None
B Only the left firefly.
C Only the right firefly.
D Both.
Explanation: It starts to get interesting after two frames:

Cavescanning order:
1. The left firefly moves right. After this, its turn is over, i.e. it does NOT explode despite the amoeba.
2. The amoeba is next. It sees the firefly to its left, but this doesn't matter -
it's the firefly that explodes when it touches an amoeba, not vice versa! So
nothing happens (we assumed that the amoeba doesn't grow).
3. The right firefly also comes closer to the amoeba.

1. Now the left firefly explodes! This means it takes the amoeba away, too,
and there are nine pieces of smoke now.
2. There's no amoeba to be scanned anymore.
3. The right firefly gets lucky - there's no amoeba touching it anymore! The
firefly sees a piece of smoke to its left, so nothing to worry about - it
survives!

Question 6

Is it possible to trap the amoeba, assuming that it doesn't grow within the
next few seconds and further assuming that the time limit is too short to let
the amoeba fill the cave?
A No, it isn't.
B Yes, Rockford must help to trap the left amoeba.
C Yes, Rockford must help to trap the right amoeba.
D Yes, both is possible.
Explanation: This is a version of cave 10 (see episode 14)! There are only
three items (including Rockford) for four places to block, so we need another
cavescan order trick! First, we do this:

Now, Rockford moves two steps right:

In the next frame, the amoeba gets trapped:
1. The top-left amoeba is blocked by the left diamond.
2. Next, this very diamond falls.
3. The top-right amoeba is blocked by Rockford.
4. The bottom-left amoeba is blocked by the diamond that has just fallen!
5. The bottom-right amoeba is blocked by the right diamond.
So the left diamond blocked two amoebas in the same frame, just as Rockford
did in cave 10!

This solution can not be mirrored, however - then the
cavescanning order would not work the same way!

Question 7

Can Rockford convert the boulder?
A No, the growing wall will block the boulder off.
B Yes,if Rockford pushes the boulder left.
C Yes, if Rockford pushes the boulder right.
D Yes, both is possible.
Explanation: Another tricky one! Actually, I got this one wrong myself at first
- I thought C was correct, and my intended solution was as follows:

If Rockford now moves down, the boulder will get past the growing wall. As
we've seen in several previous episodes - see, for example, episode 7 - for
such a thing to work, Rockford must have the growing wall at his left
side, meaning that this solution can not be mirrored.
However, there's also a possibility pushing the boulder left:

Snapping up here will also take the boulder through - see episode 3 where
this very trick was analysed! So actually, D is the correct answer!

Question 8

Rockford has already collected enough diamonds, but on his way to an
outbox, a firefly chases him closely!
Which outbox should Rockford head for?
A Top-left
B Top-right
C Bottom-left
D Bottom-right
E It doesn't matter - Rockford explodes immediately!
Explanation: It's possible to touch a firefly from its left or top side without
exploding, because then Rockford will be scanned before the fly and can still
escape. That's why Rockford does not explode immediately but can run up to
the fork. Where to turn there? If he turns right, he will touch the fly from
right and get crushed, but turning left is safe. With the same reasoning, he
must turn up at the second fork!

Question 9

What can Rockford do to survive?
[Remark: Note the facing directions of each firefly!]
A Move up
B Move left
C Move right
D Move down
E Stand still
Explanation: Let's analyse the cavescanning order:
1. The top firefly is first and moves down, now touching Rockford.
2. The left firefly is next and moves left, away from our hero.
3. Next, it's Rockford's turn, so he actually "sees" the following between-the-
frames-picture

(Note that this is a virtual picture taken between the frames, so this picture is
actually invisible for the player!)
Rockford must decide what to do. Now it's obvious that moving left is the only
option not to touch a firefly. Instead, moving right or down would mean
running into a fly that has yet to be scanned and will explode, and standing
still would mean the top firefly will explode next frame!

Question 10

Is this cave solvable with 1 diamond required?
A Yes
B No
Explanation: The only option is to move down, up, up, but then the right
boulders will fall, so the diamond cannot be collected. See also episode 5.

Question 11

Which of the following things can Rockford do without getting blocked by the
growing wall?
A Move up and immediately down again
B Move right and immediately left again
C Move down and immediately up again
D None of the above
Explanation: That's exactly the trick analysed in episode 4!

Question 12

Which of the following things can Rockford do without getting blocked by the
growing wall?
A Move up and immediately down again
B Move left and immediately right again
C Move down and immediately up again
D None of the above
Explanation: As already mentioned before, the growing wall has to be at
Rockford's left side for any similar tricks to work, so nothing will work here!

That's it! How many correct answers do you have? I don't want to value your
result and leave it up to you to judge whether you're satisfied with it!

In the next episodes, we will discuss more of the mini caves - there's still a lot
to discover!

Dustin · Post by **Dustin** » Fri Jul 31, 2020 1:18 pm

Episode 18 - cave 12 and 13 analysis, more interesting videos
https://www.youtube.com/watch?v=7-3oOxrxLD8
Cave 12 ("Sudden Death") starts at 0:11.
Cave 13 starts at 0:27.

Cave 12
The only visinle cavescan order effect here is that Rockford touches a firefly
from left without exploding, which can't surprise us anymore! Unfortunately,
the main idea behind this mini cave can't be seen in the video because it only
occurs in failure attempts: If Rockford would keep moving left, he would then
suddenly explode for no apparent reason. This is an open-border effect! Later
in this thread, we'll see more of this topic, so let's skip this one for now.

Cave 13
Funnily, the solution in the video was not my intended one, but it still uses a
very nice cavescan order effect!
Here's the map:

What do we see?
Obviously Rockford must kill the butterfly to complete the cave. But there's a
problem: Once Rockford opens the flies' cages, the firefly comes out first and
it seems impossible to prevent it from touching a voodoo. And indeed, that's
what we see in the solution - the firefly touches the voodoo, but Rockford still
survives! How is this possible? With the cavescanning order, of course!

Question 1 - why does the firefly come out first?
This one should be simple for us to answer! The decisive moment is when
both flies are ready to come out:

The cavescanning order says that the firefly is first, so it has the "right of
way" before the butterfly!

Question 2 - how does Rockford survive although a firefly touches a
voodoo?
To understand this, we first have to know the exact voodoo rules most
BD engines use:
1. If a fire-or butterfly is scanned and sees a voodoo beside it, it explodes.
In this case, Rockford explodes in the next frame as well.
2. If a voodoo explodes by any other cause, Rockford is not harmed.
To see how this works, let's see the picture immediately before the explosion:

Cavescanning order:
1. Rockford is first, but it doesn't matter what he does.
2. The voodoo is next. As the voodoo rules say, it does NOT explode, because
it's the fireflies' "job" to do that when it's scanned!
3. Next comes the falling boulder. It "sees" the butterfly below and kills it.
This means that the firefly, the boulder and the voodoo vanish in the explosion
as well!
This basically ends the scanning for this frame - the firefly and the butterfly
got crushed before they were scanned!
What can we conclude? The voodoo has exploded in step 3, but it was NOT
because the firefly touched it, but because a butterfly got crushed by a
boulder and the voodoo was inside the explosion area! So rule 2 of the
above voodoo rules applies and Rockford survives!

Interesting BD caves using cavescan order effects!
Arno has created some very challenging and creative puzzles based on a trick
we saw in episode 5:
https://www.youtube.com/watch?v=0Istmyw5nAs
https://www.youtube.com/watch?v=qXehXwwbgY0
In these caves, Rockford can control whether the left or the right element falls
first, and he has to act thoughtfully to get the formation he needs in the end!
I remember I had a lot of fun to solve these caves with big paperwork!

And here are two caves by Darkstoorm using the "safely kill voodoos" effect
we just discussed:
https://www.youtube.com/watch?v=8JuRrq0eaeM
https://www.youtube.com/watch?v=mWoZCrc_D2U
Make sure to check these out if you haven't done this already!