Block Lattice

Every account address corresponds to a chain of blocks. Each block's Previous field points to the hash of the preceding block. The first block has Previous set to "0".

Cross-Chain Links

Transfers require two blocks:

1. A send block on the sender's chain debits the sender (creates a pending send)
2. A receive block on the recipient's chain credits the recipient (consumes the pending send)

The sender and receiver do not need to be online at the same time.

Alice            Bob              Carol
┌─────────┐      ┌────────┐      ┌─────────┐
│ claim   │      │ recv   │      │ claim   │
│ bal: 10 │      │ bal: 5 │      │ bal: 10 │
└───┬─────┘      └───┬────┘      └───┬─────┘
    │                │               │
┌───▼─────┐      ┌───▼────┐      ┌───▼─────┐
│ send    │─────▶│ recv   │      │ send    │
│ to: Bob │      │ src:   │      │ to: Bob │
│ amt: 5  │      │ bal: 10│      │ amt: 3  │
│ bal: 5  │      └───┬────┘      │ bal: 7  │
└─────────┘          │           └─────────┘
                 ┌───▼────┐
                 │ recv   │◀── from Carol
                 │ bal: 13│
                 └────────┘

Properties

• No contention between accounts (parallel processing)
• Instant finality for non-conflicting transactions
• Compact representation (122–226 bytes per block)

Differences from Nano

• Dual assets (XE and XUSD)
• Additional block types (lease, lease_accept, lease_settle)
• State chain for governance
• blake2b PoW as anti-spam
• Voting weight from XUSD balances only

Block Types

Ten block types are defined: