In the short/medium term, Kakarot will exist as a smart contract embedded in Starknet, Starkware's L2 validity rollup. It will provide users with a zkEVM encapsulated inside a smart contract.

In the long term, we envision Kakarot to be Starknet's first L3.

Elias Tazartes (Eikii)

# Will Kakarot be an L3 on top of the Starknet validity rollup?

Will Kakarot be an L3 on top of the Starknet validity rollup?

What is the extension that shows you errors before compilation ser?

Which is this extension that shows you errors before compilation ser?

does anybody have a working local setup ? I find myself having to run tests on the testnet...

I tried both nile and protostar. the problem is that I can set it up but I don't know how to get access to the accounts that are pre-loaded with ETH. new accounts that I create don't have ETH and I don't have a way to transfer ETH to them..

if anybody has a go-to setup that they can share that'd be much appreciated 🙏

How to setup local Starknet node with Account contracts?

Hi everyone, I have a technical question:

We know that L2s are taking transaction load off of the Ethereum, but how is that process taking place? Is there a threshold of optimum transaction speed/cost? Are L2s only intervening when the L1 is congested or that threshold is passed?

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

 Is there a threshold of optimum transaction speed/cost in L2s?

Hello! This is day 10 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Bitwise operations”.  Perhaps you can help me?

```
// The bitwise builtin allows you to perform bitwise operations
// (and, or, xor) on integers up to 251 bits.
//
// The following code implements the function xor_last_hex_digits,
// which takes the two last hexadecimal digits and "xor"s them.
// For example, in 0x1234 the last two digits are 3 and 4,
// and their xor is 3^4=7.
//
// Fix the missing code and make sure it works.

%builtins bitwise

from starkware.cairo.common.bitwise import bitwise_and, bitwise_xor
from starkware.cairo.common.cairo_builtins import BitwiseBuiltin

// Returns the xor of the last two hexadecimal digits.
func xor_last_hex_digits{bitwise_ptr: BitwiseBuiltin*}(x: felt) -> (res: felt) {
    // Fix and uncomment the line below.
    // let (digit0) = ...

    let (shifted_digit1) = bitwise_and(x, 0xF0);
    tempvar digit1 = shifted_digit1 / 0x10;

    return bitwise_xor(digit0, digit1);
}

func main{bitwise_ptr: BitwiseBuiltin*}() {
    let (res) = xor_last_hex_digits(0x1234);
    assert res = 7;

    return ();
}
```

---

> 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 make Bitwise operations in Cairo Lang using %builtins bitwise, bitwise_xor?

I am working through [ex03](https://github.com/starknet-edu/starknet-cairo-101/blob/main/contracts/ex03.cairo) of starknet-cairo-101 and I noticed that I was not being charged a gas fee for calling `increment_counter` multiple times back to back, it only charged me once. Does anyone know why this is happening?


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/788)_

Did not have to pay gas fee when calling same function multiple times in Starknet?

I have the following code:


`from starkware.cairo.common.uint256 import Uint256`


`﻿`


`func main():`


 `test()`


 `return()`


`end`


`﻿`


`func test() -> (res : felt):`


 `alloc_locals`



 `local a : Uint256 = Uint256(low=1, high=0)`


 `if 1 == 1:`


 `local a : Uint256 = Uint256(low=2, high=0)`


 `end`



 `return (res = a)`


`end`


`﻿`


But I keep getting Error: code:20:19: Reference 'a' was revoked.


 return (res = a)


 ^


What is a good pattern for solving this issue?


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/855)_

Cairo: How to reassign Uint256 in a conditional

Is there any other way to do 2**n without using `pow.cairo`?

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Will Kakarot be an L3 on top of the Starknet validity rollup?

Will Kakarot be an L3 on top of the Starknet validity rollup?

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