# Single-Sided Tokens¶

The proposed upgrade fundamentally changes the meaning of pool tokens in AMMs. The AMM pool token concept, or “smart token”, was introduced by Bancor with its initial whitepaper and persists essentially unaltered to the present day. The concept was built around the assumption that liquidity providers would participate in both sides of the pool; however, with the introduction of single-sided staking by Bancor, a revision of the pool token idea is overdue. Bancor v2.1 still makes use of traditional pool tokens, although their role in the system is permanently obscured from view. A plethora of auxiliary mechanisms are required to support single sided staking, which can largely be replaced by a purpose-built system that assumes the contribution of only one token, rather than two or more.

Single-Sided Tokens Tokens express themselves in the simulator code via the Transaction class definition.

Note that the Transaction itself can only track one tkn_name balance at a time.

Even so, notice that the ledger automatically pairs the single-sided token with BNT, providing a true utility behavior as a global medium of exchange between all other pool tokens.

In a later chapter we will discuss the other Ledger classes of the protocol.