Does the connection between 'If you need this book, it is probably too late' unless you are about to take an SAT or GRE.' and 'It's probably too late unless you're going to take an SAT or GRE, then you need this book.' lack any definitive logical relationship?
If you need this book, it is probably too late' unless you are about to take an SAT or GRE.###It's probably too late unless you're going to take an SAT or GRE, then you need this book.