Gasless crypto exchanges: How to swap tokens without transaction fees?

The gasless feature is currently only available on the development stand, we developed it as research but yet implemented it on the protocol level.
Problem
To perform any operations with assets, the user must also have native blockchain coins to pay transaction fees, which is a quite common but not ideal UX. The scenario becomes especially noticeable when a user must simultaneously perform transactions on different blockchains. For example, immediately after the exchange UNI ERC-20 -> CAKE BEP-20, the user will not be able to use the received asset until he replenishes the BNB wallet — and so on with every network on which he or she has liquidity.
Imagine a situation when you want to withdraw you LP on Pangolin AMM which located on Avalanche and ran out of AVAX for gas fees. Or situation when you don't want to spend you ETH on gas fees for USDT<>UNI swap.
Solution
To solve the problem, we propose using a gasless approach — withholding transaction fees on the blockchain by exchanging tokens with a positive wallet balance. These can be a token exchange scenario or a simple sending scenario.
This situation can be solved by Gasless feature that will allow users to pay the gas fees in an asset they are swapping, in case of USDT:UNI swap you will be able to pay gas fees with USDT. This will tremendously improve user experience for users interacting with multiple chains.
For tokens that support the permit method, it is possible to use the gasless approach without restrictions; for all other cases, we suggest using a single stable coin sisUSD with permit support on all networks.
The exchange takes place in on-chain and cross-chain pools, such as sisUSD <> ETH, sisUSD <> BNB, sisUSD <> AVAX etc.
Also, SIS tokens can be used as gasless tokens as well as other ERC20 tokens.
How it works 

A great starting point to understand gasless transactions is https://docs.opengsn.org/#the-problem​
We currently using opengsn.org as a infrastructure layer and our concentrated pools to settle paymaster transactions.

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Outline

Problem

Solution

How it works