#7: adjusted simple past and present perfect definitions to match both, Nikhil's clarifications in the email and the examples in the PDF. Without this adjustment 'John ate' at w2 would, in contrary to the PDF, not enforce 'John eats' to be true at w1 (it could just be true at w2). Wit hthe new definition of simple past and present perfect, the same event MUST be true in present-tense at some earlier point in time and CAN be true now for simple past vs CANNOT be true now for present perfect