  The asset trading volume on blockchain-based exchanges (DEX) increased
substantially since the advent of Automated Market Makers (AMM). Yet, AMMs and
their forks compete on the same blockchain, incurring unnecessary network and
block-space overhead, by attracting sandwich attackers and arbitrage
competitions. Moreover, conceptually speaking, a blockchain is one database,
and we find little reason to partition this database into multiple competing
exchanges, which then necessarily require price synchronization through
arbitrage.
  This paper shows that DEX arbitrage and trade routing among similar AMMs can
be performed efficiently and atomically on-chain within smart contracts. These
insights lead us to create a new AMM design, an Automated Arbitrage Market
Maker, short A2MM DEX. A2MM aims to unite multiple AMMs to reduce overheads,
costs and increase blockchain security. With respect to Miner Extractable Value
(MEV), A2MM serves as a decentralized design for users to atomically collect
MEV, mitigating the dangers of centralized MEV relay services.
  We show that A2MM offers essential security benefits. First, A2MM strengthens
the blockchain consensus security by mitigating the competitive exploitation of
MEV, therefore reducing the risks of consensus forks. A2MM reduces the network
layer overhead of competitive transactions, improves network propagation,
leading to less stale blocks and better blockchain security. Through trade
routing, A2MM reduces the predatory risks of sandwich attacks by taking
advantage of the minimum profitable victim input. A2MM also offers financial
benefits to traders. Failed swap transactions from competitive trading occupy
valuable block space, implying an upward pressure on transaction fees. Our
evaluations shows that A2MM frees up 32.8% block-space of AMM-related
transactions. In expectation, A2MM's revenue allows to reduce swap fees by 90%.
