> At every place X in the following expression, introduce a boolean negation if there isn’t one (or, equivanently remove one if there is), and I think it shoul

> At every place X in the following expression, introduce a boolean negation if there isn’t one (or, equivanently remove one if there is), and I think it should read: At every place X in the following expression, introduce a boolean negation if there isn’t one and remove one if there is, and Maybe even better: At every place X in the following expression, introduce a boolean negation. If you get two concecutive NOT's, they can be removed. Next, I don't see how timespent <= duration is the negation of duration > time_spent ?