Hell no. Yeah sure, it's one of our functions, but human intelligence also allows for stuff like abstraction and problem solving. There are things that you can do in your head without using words.
Not an advanced mathematician, but I think it's just saying that f(x-delta) between f(x + delta) is going to give a value between L - epsilon and L + epsilon.
Not a song but the sonic 3 & knuckles miniboss theme goes incredibly hard.
Still used by many to represent Eggman