author: Wiggins LYU & William LIU
ERC-406 protocal is a improved protocal developed based on ERC-404. ERC-404 protocol as we know, is a protocol that break NFT into ERC-20 token pieces some how. And make NFT more easy to trade and solve the liquidity problem among ERC-721 tokens. ERC-406 add a stages upgrading machanism into ERC-404 protocol.