There is a bridge between Mainnet <-> ERC-20 which makes it possible to travel from one side to another. A bridge troll in-between manages the flow of tokens and punishes early sell-offs. It protects the community during the first 6 months (since launch in January 2019) and burns the tokens, according to a dynamic fee which should be counted since January 17, 2019: . Once someone goes from mainnet to ERC20, and gives 40 LTO to mainnet nodes if someone goes from ERC20 to mainnet.
LTO mainnet are not directly tradeable but can come into or leave the network via the bridge. For liquidity purposes, LTO ERC-20 tokens are used. The LTO tokens and LTO ERC-20 tokens share the same supply. They can be exchanged for each other using the bridge in a 1:1 ratio.
ERC-20 -> Mainnet: 40 LTO for crossing the bridge. Given to mainnet nodes.
Mainnet -> ERC-20: dynamic fee is taken and is forever burned.