Ensuring the uniqueness of transactions is a critical step in the verification process, preventing:

1. Double-spending: Ensuring that the same funds are not spent twice.

2. Duplicate transactions: Preventing identical transactions from being processed multiple times.

To check for uniqueness, nodes and validators use various techniques, including:

1. Transaction hashes: Verifying that each transaction has a unique hash.

2. Transaction IDs: Checking that each transaction has a unique ID.

3. Input and output tracking: Verifying that the inputs and outputs of each transaction are unique and not already spent.

4. Blockchain state: Checking the current state of the blockchain to ensure that the transaction is not a duplicate or already spent.

By ensuring the uniqueness of transactions, the blockchain network can:

1. Prevent financial fraud and errors.

2. Maintain the integrity of the blockchain state.

3. Support the security and reliability of the network.

4. Enable trustless and efficient transactions.

In summary, uniqueness checking is a vital step in the transaction verification process, ensuring that each transaction is processed only once and preventing potential fraud and errors.