    fn swap_2_internal(
        pools: &mut Pools,
        from: Address,
        to: Address,
        amount: U256,
        min_out: U256,
    ) -> Result<(U256, U256, U256, I256, i32, i32), Revert> {
        let original_amount = amount;

        let amount = I256::try_from(amount).map_err(|_| Error::SwapResultTooHigh)?;

        // swap in -> usdc
        let (amount_in, interim_usdc_out, final_tick_in) = pools.pools.setter(from).swap(
            true,
            amount,
            // swap with no price limit, since we use min_out instead
            tick_math::MIN_SQRT_RATIO + U256::one(),
        )?;
        ...
    }
    pub fn swap_2_internal_erc20(
        pools: &mut Pools,
        from: Address,
        to: Address,
        amount: U256,
        min_out: U256,
        permit2: Option<Permit2Args>,
    ) -> Result<(U256, U256), Revert> {

        let (
            original_amount,
            amount_in,
            amount_out,
            _interim_usdc_out,
            _final_tick_in,
            _final_tick_out,
        ) = Self::swap_2_internal(pools, from, to, amount, min_out)?;

        // transfer tokens
        erc20::take(from, original_amount, permit2)?;
        erc20::transfer_to_sender(to, amount_out)?;

        Ok((amount_in, amount_out))
    }
}
    pub fn swap_2_internal_erc20(
        pools: &mut Pools,
        from: Address,
        to: Address,
        amount: U256,
        min_out: U256,
        permit2: Option<Permit2Args>,
    ) -> Result<(U256, U256), Revert> {

        let (
            original_amount,
            amount_in,
            amount_out,
            _interim_usdc_out,
            _final_tick_in,
            _final_tick_out,
        ) = Self::swap_2_internal(pools, from, to, amount, min_out)?;

        // transfer tokens
        erc20::take(from, original_amount, permit2)?;
        erc20::transfer_to_sender(to, amount_out)?;

+       if(original_amount > amount_in){
+           erc20::transfer_to_sender(to, original_amount - amount_in)?;
+       }

        Ok((amount_in, amount_out))
    }
}
