Yes, I believe J.Y. made a typo it should be I → C (choosing to negate the implementation) So becomes not I --> not C

Here's an example to help explain this:

Low Quality Tea (before tariff) = $5

High Quality Tea (before tariff) =$10

Tariff = $2

Low Quality Tea (before tariff) = $7

High Quality Tea (before tariff) =$12

In this example the low quality tea still has a lower price than the high quality tea. I think you are assuming that the low quality tea and high quality tea both start at the same price, when that maybe is not the case

Interested!

Reading through the comments on the video explanations helps me. Don't be afraid to ask a question in the comments section of the video if you're still confused. This community is really great and if you ask a question, someone will respond and help you work through it.