# Challenge Initiation

Once a **Validating Node (VN)** detects a discrepancy, it initiates a challenge. For the challenge to proceed, the VN must provide clear **proof** to justify the challenge. This proof is essential to ensure that the challenge is valid and is not raised without substantial evidence.

<figure><img src="/files/cjyOhIcgOZs4YGVuK5TG" alt=""><figcaption><p>Challenge Initiation</p></figcaption></figure>

## **Proof Required for Different Discrepancies**

### **Incorrect Sequencing of Orders by the Off-Chain Sequencer**

If the discrepancy is related to incorrect sequencing, where the sequencer has processed orders in the wrong order, the VN must provide timestamps and data logs from both the **off-chain sequencer** and **on-chain data**.

**Proof Required**:

* **Order timestamps** from the sequencer that show when each transaction was received.
* A log of the actual **order sequence** processed by the sequencer.
* Comparison of the timestamps to show the correct sequence of events (e.g., that **Order B** should have been processed before **Order C**, but the sequencer processed **Order C** first).
* The corresponding **on-chain (Submission B) records** showing the mismatch, if relevant.

**Example**: The VN submits proof showing that:

* **Order B** was received at **10:01 AM** and **Order C** at **10:02 AM**.
* The sequencer, however, processed **Order C** first, even though it arrived later. This would be enough evidence for the challenge to pass to the next phase.

***

### **Mismatch Between On-Chain and Off-Chain Data**

If the challenge is due to a mismatch between the off-chain order and its corresponding on-chain transaction, the VN must present proof comparing the two sets of data, showing the inconsistency between what was processed off-chain and what was posted on-chain.

**Proof Required:**

* **Off-chain (Submission A) transaction logs** that include the details of the transaction as processed by the sequencer.
* **On-chain (Submission B) transaction data** as posted on-chain, such as amounts, transaction IDs, and other relevant information.
* A **comparison of both off-chain and on-chain data** to show the discrepancy (e.g., an on-chain order for **1 BTC** is posted off-chain as **0.5 BTC**).

**Example:**

A VN provides evidence showing that:

* The off-chain record for **Order A** was to sell **0.5 BTC** for **1 ETH**.
* The on-chain record for **Order A** shows **1 BTC** for **1 ETH**.

This mismatch between off-chain and on-chain data would serve as valid proof for the challenge.

### **How Submission B Helps Identify Mismatches?**

When orders are posted directly on-chain through the **Submission B** method, these mismatches can be easily identified. Since **Submission B** directly records the order on the blockchain without going through the centralized sequencer, it provides a clear, immutable source of truth. VNs can compare the data from **Submission B** (the on-chain version) with the off-chain logs processed by the sequencer. Any discrepancies between the two would immediately stand out, making it straightforward for VNs to detect and challenge errors.

***

### **Exclusion of Valid Orders**

If the sequencer has excluded an order that should have been processed and posted on-chain, the VN must prove that the order was submitted but was not included on-chain.

**Proof Required**:

* **Proof of submission** that the order was valid and was submitted directly **on-chain (Submission B)**, along with the exact details (e.g., order details, submission time).
* A check of the **off-chain** records proving that the order was never included or posted by the sequencer **(Submission A)**.

**Example**: If **Order A** (sell **1 BTC** for **1 ETH**) was submitted directly on-chain and never processed by the sequencer, the VN provides logs showing the order was received directly on-chain but was not processed by the sequencer. This would serve as evidence of the exclusion.


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