you can cancel anytime prior to the message being consumed, so potentially if you sent a message by mistake and were quick enough

_This answer was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Newton

When it comes to message cancellation (L1 -> L2) you can cancel a message in the case that:
- There is any kind of censorship on StarkNet (sequencer skipped your tx)
- The L2 contract's `` function flow has an assert that fails

Is this correct? Am I missing any other situations where message cancellation would/wouldn't work?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Can you explain about cancellation (L1 -> L2) in StarkNet (sequencer)?

My Alchemy dashboard usage is low?


In SNARKs, you can use [Zokrates](https://zokrates.github.io/gettingstarted.html#hello-zokrates) or [snarkjs](https://github.com/iden3/snarkjs) to generate a proof for a program/computation and verify it, locally or on Ethereum.


Similar to [this unanswered question](https://github.com/starkware-libs/cairo-lang/issues/2), how to do the same in Cairo and STARK for, say, [the 15-puzzle](https://www.cairo-lang.org/docs/hello_cairo/puzzle.html)?


Can `cairo-run` generate a proof, or only a trace?


I can send it to [SHARP](https://www.cairo-lang.org/docs/sharp.html) with `cairo-sharp`, but I can't generate nor see the proof locally. Any way to generate the proof by running my own prover without SHARP?



ㅤ
_This question was originally posted on [Stack Overflow](https://stackoverflow.com/questions/73056271/how-to-generate-a-proof-for-a-cairo-program-and-verify-it)_

How to generate a proof for a Cairo program and verify it?

Hello! This is day 17 of the 17 days of the Cairo Challenge. In this challenge I want to ask you [install](https://www.cairo-lang.org/docs/quickstart.html) Cairo and try to launch your first program. What have you implemented as your first Cairo language program?

**Step 1**
```solidity
// 1. Make sure that you installed dev packages on your device
sudo apt install -y libgmp3-dev // Linux
brew install gmp // Mac OS
```
**Step 2**
```solidity
// 2. Install Cairo using Python virtual environment
python3.9 -m venv ~/cairo_venv
source ~/cairo_venv/bin/activate
pip3 install ecdsa fastecdsa sympy;
pip3 install cairo-lang;
```
**Step 3**
```bash
// 3. Make sure you have python 3.9. Because Cairo was tested with python3.9. To make it work with python3.6, you will have to install contextvars:
pip3 install contextvars
```
**Step 4**
```python
// 4. Write your program
// Create a file, named hello.cairo, with the following lines:
 
func main() {
		// edit me: you can add here any output, best program wins the challenge
    ret;
}

```solidity
//5. Compile your program
cairo-compile hello.cairo --output hello_compiled.json
```
**Last step**
```solidity

//6. Run:
cairo-run \
  --program=hello_compiled.json --print_output \
  --print_info --relocate_prints

//7. Debug:
//You can open the Cairo tracer by providing the --tracer flag to cairo-run. Then open it at http://localhost:8100/.
```
If you have questions, create them on Newton and we will help!

---
> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to install Cairo v0.10.0 on my device?

Hello guys, does one know how to modify keccak.cairo and/or packed_keccak.cairo to compute a 512bits keccak hash instead of 256 bits?

I'm following a paper that needs 256 bits collision resistance so i need 512 bit keccak. 

There should only a few parameters to change but its quite hard to find them in the Cairo code 

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

---

This question is participating in [Newton Bounties | Incentivized Test Program](https://www.notion.so/Newton-Bounties-Incentivized-Test-Program-94322ad48e7d40a3adcf36f6b26174cd) Every verified valid question gets $10 USDC (mainnet)

How to modify keccak.cairo and/or packed_keccak.cairo to compute a 512bits keccak hash instead of 256 bits?


How to verify Empiric’s Data Entries Using Events?

I'm trying to use Nile (StarkNet).
I send this function call : 

```cairo
func setBaseURI{pedersen_ptr: HashBuiltin*, syscall_ptr: felt*, range_check_ptr}(
    baseUri_len: felt, baseUri: felt*
)
```

The only thing that would get processed is 

```
nile send account mycontract setBaseURI 3 1 1 1
```

but I don't think that's the right way. How do you pass an array of felt to call with Nile?

How can I pass an array of felt to call with Nile in StarkNet?

Another vanilla Cairo question, what are the sorts of references, i.e. ids that can be modified by hints? relatively important to work against an evil prover

presumably not locals or tempvars, but say, implicit references, or the two(?) kinds of let statements (expressions and references)

maybe if there's some documentation i don't know about re: all the id types, relocatable values and so on,

also maybe, is there a pattern that can be used for function pointers?

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Can you explain about cancellation (L1 -> L2) in StarkNet (sequencer)?

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