The Invariant

At its core, Aspan Finance is a Risk Tranching Protocol. We pool underlying BNB staking assets (LSTs) into a unified vault, then split their value into two parts:

1. Hedged Risk Tranche: Generates the stablecoin apUSD.

2. Residual Risk Tranche: Generates the leverage token xBNB.

This split caters to two distinct user needs: users seeking stable yields (apUSD) and users seeking high-leverage exposure to price volatility (xBNB).

Unlike most protocols that rely on external DEX liquidity to price tokens, Aspan maintains an internal accounting invariant that serves as the cornerstone of all protocol pricing. TVLUSD=(SupplyapUSD×$1.00)+(SupplyxBNB×PricexBNB)

• TVLUSD: The real-time total USD value of all collateral (slisBNB/BNBx) in the vault.

• apUSD: The liability side of the system, which the protocol always values at $1.00.

• xBNB: The equity side of the system, representing the residual value of the vault after deducting liabilities (Variable Reserve).

🔄 How Does It Work? Imagine a water tank:

• Water Volume (TVL): As BNB’s price rises or falls, the water volume (total value) in the tank fluctuates.

• Fixed Base (apUSD): The bottom of the tank is a fixed stone with a constant volume (value pegged to $1).

• Top Space (xBNB): The remaining water level space belongs to xBNB.

When the total water volume increases, the fixed base remains unchanged, and all incremental value is added to the top space—that’s the mathematical principle behind xBNB’s leverage effect.