:up: This is interesting - the 'default direction' for page-turning is forwards. We say 'turn back a page' when we mean back, but just 'turn a/the page' when we mean forwards. This is especially true when 'turn a page' is used metaphorically: 'He used to be a homeless drug-addict, but now he's turned the page'; 'This is going nowhere. We both need to turn a page and move on' - that sort of page turning is always progress (not regression).
b