# 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.

Challenge Initiation

## **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.