And to resort to the squeeze theorem, you just have to view c as a function of delta x. And it really is. Depending on your delta x, c is going to be further to the left or to the right, possibly. And so I can just rewrite this expression as x is less than or equal to c as a function of delta x, which is less than or equal to x plus delta x. So now you see that c is always sandwiched between x and x plus delta x. Well what's the limit of x as delta x approaches 0? Well x isn't dependent on delta x in any way.