it appears I wasn’t the only one who misunderstood when the instructor said “lose your money” thanks for clarifying group. 
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I have a question, if someone could provide a clarification on the update process.
Who will propose changes or suggestions of updates? I read the BIP description, and it’s not clear to me how the changes are proposed, by whom, and how the decision to accept or not an update works.
Any suggested reading for me, or clues to help me understand?
Thanks in advance
No, I didn’t, but I will now. 
Thank you!
I don’t think it is mentioned, but is it true that forks are used to counter hackers?
They can be. Ethereum had a hard fork way back in its infancy that was used to reverse transactions from the DAO hack. It was also the reason why the network split in Ethereum and Ethereum classic.
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Hehe okay thanks. I remember it from an Ethereum documentary that i’ve seen, but i suppose it’s not a common thing for every network then.
Hello everybody,
I don’t get it. How can the blockchain/bitcoin get updatet? Who make these kind of updates? How can the nodes become a update?
Because for me, from this Bitcoin topic: I’ve learned that it is decentralized, has nobody who controlles, just consensus and has it own clear rules, proof of work et cetera…
Thanks for that ^^
Hi, In the videos of stale blocks and forks, the examples are allways with two blocks being created at the same time.
I’m guessing that this same thing could happen with multiple blocks being created at the same time, lets say 3, 4, 5…blocks or more. Would that be possible?
The community discusses the upgrades and are eventually implemented if accepted. The process is described in BIP1.
Of course it is possible. This is why the rule of thumb is to wait 6 confirmations by that time the probability of this still being the case is basically 0 (its never quite, but that is statistic for you 
).
Alright, thank you
- Given there is a fork due to updated and non-updated nodes, I assume it is the blockchain that doesn’t contain the update that is “orphaned” or made stale?
Hi Filip,
With regards to the first question on the quiz, I felt that both C and D were right answers, weren’t they? They were blocks submitted by different miners at the same block height at the same time ©, but those blocks will also have had different content, i.e. different TXs within the block (D)? Thanks
The answers I think are randomized so I’m not sure which are you referring to exactly. Its a bit of a trick question and only one is correct. The blocks must be different on the same height.
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Hi @filip , I don’t get what you mean when you say that ‘‘you want to make sure that your transaction is not in the green (STALE) block (min. 8.00) or you will loose your money’’.
Aren’t the transactions going back to the mempool and get in a new block sooner or later ??
How can we avoid that by the way, we’re not miners and we just made a transaction.
Dear Filip,
The explanation you gave in the course minute 08:17 with the ‘loose of your money’; I’ve already relistened to it several times, read the comments in this posting and it is getting even more confusing. In order to get it explained in a simplified way, I will break it down into steps, the way I understood the process so far:
- I have a wallet, I access it and initiate a transaction, let’s assume I want to buy a few EGLD with the amount of BTC I have available.
- I send the request of buying/place the order, it reaches a series of nodes, nodes check the availability in the sense I have enough BTC to buy the desired amount of EGLD. They say ok, accept the transaction/it makes sense, it is then sent to a mempool and is waiting there for a miner to come, to pick up the TX, include it into a block and start guessing the nonce - first thing that is not clear here, as it is broadcasted to several nodes, thus included in their mempools and used for mining, the miner that solves the puzzle is the one that is using it to be written in the blockchain, right? the TX itself travels across various nodes, it’s picked up by let’s say 2 miners, it travels further to their blocks, and utilized for mining; once the puzzle is solved, by let’s say both of them, the TX coexist in both blocks and it awaits for the validation of the next miner that manages to prove the longest chain/most PoW, once it’s validated it “makes it” to the blockchain and it’s written then in stone; what happens then to the TX from the unsuccessful block that didn’t make it to the blockchain, basically the block it’s dropped and all transactions are sent back to the mempools. There are few things that are blurry or my understanding is limited, if you or Ivan could explain better it would be of great help.
Another statement that is confusing, what does it mean in this reply to the post: "If the sender has bad intent and removed the tx from the mempool, you as a receiver of crypto have now lost your money. " The sender cannot just go to the mempool, the nodes are the ones who eventually can do it, but you cannot remove it, once it’s out, it is out. What am I missing here?
All in all, it would be of great help if you would align this explanation, because now, what I thought I kind of understood from Ivan is contradicted by your statements. A real-life example would be of great, great help. Just to follow a simulation of a TX, from the beginning to the end. And to explain it along the way, what is it that is going on in the background of the process. One step at a time.
Thank you.
Best regards,
Sheila.
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You don’t really loose the transaction but in case its dropped back to the mempool, the sender can then broadcast a new tx using the same UTXOs with a higher fee, ensuring the tx will be mined first thus invalidating the original tx.
If the transaction is mined in both blocks then there is no issue, but at the time there is no way of knowing for sure weather your tx is included in both blocks.
Once the fork is resolved the nodes return transactions that were not in both blocks back to the mempool. When they are returning these transactions they validate them again if a tx was also part of the winning block it would mean its UTXOs are spent and the tx would be invalid (or already confirmed in another block) and not returned back to the mempool.
thank you for the input, it doesn’t really answers my question or at least for me it it not cistal clear.
Since it creates so much confusion, it would be good to clarify by simulating a transaction, one for the second layer users like me/who only buys coins, and another one for a company that uses blockchain in their current business. As a wrap up of the whole chapter, with all the information, which at times is complicated enough, I should be able to explain in my words what the process look like every step of the way, only then information can be classified as ‘learned’, until then i didn’t quite ‘got it’. I address to Ivan or Filip, please support this course with an appendix of a simulation, the same way Ivan wrapped things up in few minutes, before Filip took over in this course. Thank you.
@Alko89 cheers for the reply but this is still a bit confusing for me too.
You said the sender can then broadcast a new tx using the same UTXOs with a higher fee … does the sender have to do that or can he just wait for the orignal transaction to go through in the next block ? … I mean without paying the extra fee.
Once a transaction goes back to the mempool does the sender get a notification ??
How can you invalidate the original TX ? I thought transactions were impossible to modify and once they are done - they are done.
Sorry but I’m new to this.