There's a lot of introduction here, but it starts getting to the point in section 3.4 "The previous paper". That paper is "A Relatively Small Turing Machine Who

There's a lot of introduction here, but it starts getting to the point in section 3.4 "The previous paper". That paper is "A Relatively Small Turing Machine Whose Behavior Is Independent of Set Theory" https://arxiv.org/abs/1605.04343 https://arxiv.org/abs/1605.04343 (and an improvement in the blog comments on https://scottaaronson.blog/?p=2725 https://scottaaronson.blog/?p=2725) I recommend starting there just to know where the conversation is going and then coming back to this.