We know that it is continuous over the closed interval between x equals a and x is equal to b. And so when we put these brackets here, that just means closed interval. That means we're including, so when I put a bracket here, that means we're including the point a. And if I put the bracket on the right-hand side instead of a parenthesis, that means that we are including the point b. And continuous just means we don't have any gaps or jumps in the function over this closed interval. Now let's also assume that it's differentiable over the open interval between a and b. So now we're saying, well, it's okay if it's not differentiable right at a, or if it's not differentiable right at b.